llvm-runtimes/libunwind: Use the partial clang configuration files

Initial installation or upgrade of libunwind happens before before the main slotted clang configuration file is created by llvm-core/clang-runtime. Building libunwind requires only the linker (`-fuse-ld`) and rtlib (`--rtlib`) configuration to be present. To fix the initial builds, we can use the partial configuration provided by llvm-core/clang-linker-config and llvm-runtimes/clang-rtlib-config. Signed-off-by: Michal Rostecki <vadorovsky@protonmail.com> Closes: https://bugs.gentoo.org/951445 Part-of: https://github.com/gentoo/gentoo/pull/42663 Signed-off-by: Michał Górny <mgorny@gentoo.org> Part-of: https://github.com/gentoo/gentoo/pull/42663 Signed-off-by: Michał Górny <mgorny@gentoo.org>
2026-01-04 13:47:35 -08:00 · 2025-08-26 19:01:00 +02:00 · 2025-08-26 19:01:00 +02:00 · a2e6ca5dd5
commit a2e6ca5dd5
parent f1d6e8dd62
4 changed files with 477 additions and 4 deletions
--- a/llvm-runtimes/libunwind/libunwind-20.1.8-r1.ebuild
+++ b/llvm-runtimes/libunwind/libunwind-20.1.8-r1.ebuild
@ -0,0 +1,193 @@
+# Copyright 1999-2025 Gentoo Authors
+# Distributed under the terms of the GNU General Public License v2
+
+EAPI=8
+
+PYTHON_COMPAT=( python3_{11..14} )
+inherit cmake-multilib crossdev flag-o-matic llvm.org llvm-utils
+inherit python-any-r1 toolchain-funcs
+
+DESCRIPTION="C++ runtime stack unwinder from LLVM"
+HOMEPAGE="https://llvm.org/docs/ExceptionHandling.html"
+
+LICENSE="Apache-2.0-with-LLVM-exceptions || ( UoI-NCSA MIT )"
+SLOT="0"
+KEYWORDS="~amd64 ~arm ~arm64 ~loong ~mips ~ppc ~ppc64 ~riscv ~sparc ~x86 ~arm64-macos ~x64-macos"
+IUSE="+clang debug static-libs test"
+REQUIRED_USE="test? ( clang )"
+RESTRICT="!test? ( test )"
+
+RDEPEND="
+	!sys-libs/libunwind
+"
+DEPEND="
+	llvm-core/llvm:${LLVM_MAJOR}
+"
+BDEPEND="
+	clang? (
+		llvm-core/clang:${LLVM_MAJOR}
+		llvm-core/clang-linker-config:${LLVM_MAJOR}
+		llvm-runtimes/clang-rtlib-config:${LLVM_MAJOR}
+	)
+	!test? (
+		${PYTHON_DEPS}
+	)
+	test? (
+		$(python_gen_any_dep 'dev-python/lit[${PYTHON_USEDEP}]')
+	)
+"
+
+LLVM_COMPONENTS=( runtimes libunwind libcxx llvm/cmake cmake )
+LLVM_TEST_COMPONENTS=( libc libcxxabi llvm/utils/llvm-lit )
+llvm.org_set_globals
+
+python_check_deps() {
+	use test || return 0
+	python_has_version "dev-python/lit[${PYTHON_USEDEP}]"
+}
+
+test_compiler() {
+	target_is_not_host && return
+	local compiler=${1}
+	shift
+	${compiler} ${CFLAGS} ${LDFLAGS} "${@}" -o /dev/null -x c - \
+		<<<'int main() { return 0; }' &>/dev/null
+}
+
+multilib_src_configure() {
+	if use clang; then
+		llvm_prepend_path -b "${LLVM_MAJOR}"
+	fi
+
+	local libdir=$(get_libdir)
+
+	# https://github.com/llvm/llvm-project/issues/56825
+	# also separately bug #863917
+	filter-lto
+
+	# Workaround for bgo #961153.
+	# TODO: Fix the multilib.eclass, so it sets CTARGET properly.
+	if ! is_crosspkg; then
+		export CTARGET=${CHOST}
+	fi
+
+	if use clang; then
+		local -x CC=${CTARGET}-clang-${LLVM_MAJOR}
+		local -x CXX=${CTARGET}-clang++-${LLVM_MAJOR}
+		strip-unsupported-flags
+
+		# The full clang configuration might not be ready yet. Use the partial
+		# configuration files that are guaranteed to exist even during initial
+		# installations and upgrades.
+		local flags=(
+			--config="${ESYSROOT}"/etc/clang/"${LLVM_MAJOR}"/gentoo-{rtlib,linker}.cfg
+		)
+		local -x CFLAGS="${CFLAGS} ${flags[@]}"
+		local -x CXXFLAGS="${CXXFLAGS} ${flags[@]}"
+		local -x LDFLAGS="${LDFLAGS} ${flags[@]}"
+	fi
+
+	# Check whether C compiler runtime is available.
+	if ! test_compiler "$(tc-getCC)"; then
+		local nolib_flags=( -nodefaultlibs -lc )
+		if test_compiler "$(tc-getCC)" "${nolib_flags[@]}"; then
+			local -x LDFLAGS="${LDFLAGS} ${nolib_flags[*]}"
+			ewarn "${CC} seems to lack runtime, trying with ${nolib_flags[*]}"
+		elif test_compiler "$(tc-getCC)" "${nolib_flags[@]}" -nostartfiles; then
+			# Avoiding -nostartfiles earlier on for bug #862540,
+			# and set available entry symbol for bug #862798.
+			nolib_flags+=( -nostartfiles -e main )
+			local -x LDFLAGS="${LDFLAGS} ${nolib_flags[*]}"
+			ewarn "${CC} seems to lack runtime, trying with ${nolib_flags[*]}"
+		fi
+	fi
+	# Check whether C++ standard library is available,
+	local nostdlib_flags=( -nostdlib++ )
+	if ! test_compiler "$(tc-getCXX)" &&
+		test_compiler "$(tc-getCXX)" "${nostdlib_flags[@]}"
+	then
+		local -x LDFLAGS="${LDFLAGS} ${nostdlib_flags[*]}"
+		ewarn "${CXX} seems to lack runtime, trying with ${nostdlib_flags[*]}"
+	fi
+
+	# link to compiler-rt
+	# https://github.com/gentoo/gentoo/pull/21516
+	local use_compiler_rt=OFF
+	[[ $(tc-get-c-rtlib) == compiler-rt ]] && use_compiler_rt=ON
+
+	# Respect upstream build type assumptions (bug #910436) where they do:
+	# -DLIBUNWIND_ENABLE_ASSERTIONS=ON =>
+	#       -DCMAKE_BUILD_TYPE=DEBUG  => -UNDEBUG
+	#       -DCMAKE_BUILD_TYPE!=debug => -DNDEBUG
+	# -DLIBUNWIND_ENABLE_ASSERTIONS=OFF =>
+	#       -UNDEBUG
+	# See also https://github.com/llvm/llvm-project/issues/86#issuecomment-1649668826.
+	use debug || append-cppflags -DNDEBUG
+
+	local mycmakeargs=(
+		-DLLVM_ROOT="${ESYSROOT}/usr/lib/llvm/${LLVM_MAJOR}"
+
+		-DCMAKE_C_COMPILER_TARGET="${CTARGET}"
+		-DCMAKE_CXX_COMPILER_TARGET="${CTARGET}"
+		-DPython3_EXECUTABLE="${PYTHON}"
+		-DLLVM_ENABLE_RUNTIMES="libunwind"
+		-DLLVM_LIBDIR_SUFFIX=${libdir#lib}
+		-DLLVM_INCLUDE_TESTS=OFF
+		-DLIBUNWIND_ENABLE_ASSERTIONS=$(usex debug)
+		-DLIBUNWIND_ENABLE_STATIC=$(usex static-libs)
+		-DLIBUNWIND_INCLUDE_TESTS=$(usex test)
+		-DLIBUNWIND_INSTALL_HEADERS=ON
+
+		# support non-native unwinding; given it's small enough,
+		# enable it unconditionally
+		-DLIBUNWIND_ENABLE_CROSS_UNWINDING=ON
+
+		# avoid dependency on libgcc_s if compiler-rt is used
+		-DLIBUNWIND_USE_COMPILER_RT=${use_compiler_rt}
+	)
+	if is_crosspkg; then
+		mycmakeargs+=(
+			# Without this, the compiler will compile a test program
+			# and fail due to no builtins.
+			-DCMAKE_C_COMPILER_WORKS=1
+			-DCMAKE_CXX_COMPILER_WORKS=1
+			# Install inside the cross sysroot.
+			-DCMAKE_INSTALL_PREFIX="${EPREFIX}/usr/${CTARGET}/usr"
+		)
+	fi
+	if use test; then
+		mycmakeargs+=(
+			-DLLVM_ENABLE_RUNTIMES="libunwind;libcxxabi;libcxx"
+			-DLLVM_EXTERNAL_LIT="${EPREFIX}/usr/bin/lit"
+			-DLLVM_LIT_ARGS="$(get_lit_flags)"
+			-DLIBUNWIND_LIBCXX_PATH="${WORKDIR}/libcxx"
+
+			-DLIBCXXABI_LIBDIR_SUFFIX=
+			-DLIBCXXABI_ENABLE_SHARED=OFF
+			-DLIBCXXABI_ENABLE_STATIC=ON
+			-DLIBCXXABI_USE_LLVM_UNWINDER=ON
+			-DLIBCXXABI_INCLUDE_TESTS=OFF
+
+			-DLIBCXX_LIBDIR_SUFFIX=
+			-DLIBCXX_ENABLE_SHARED=OFF
+			-DLIBCXX_ENABLE_STATIC=ON
+			-DLIBCXX_CXX_ABI=libcxxabi
+			-DLIBCXX_ENABLE_ABI_LINKER_SCRIPT=OFF
+			-DLIBCXX_HAS_MUSL_LIBC=$(llvm_cmake_use_musl)
+			-DLIBCXX_HAS_GCC_S_LIB=OFF
+			-DLIBCXX_INCLUDE_TESTS=OFF
+			-DLIBCXX_INCLUDE_BENCHMARKS=OFF
+		)
+	fi
+
+	cmake_src_configure
+}
+
+multilib_src_test() {
+	local -x LIT_PRESERVES_TMP=1
+	cmake_build check-unwind
+}
+
+multilib_src_install() {
+	DESTDIR=${D} cmake_build install-unwind
+}
--- a/llvm-runtimes/libunwind/libunwind-21.1.0-r1.ebuild
+++ b/llvm-runtimes/libunwind/libunwind-21.1.0-r1.ebuild
@ -0,0 +1,194 @@
+# Copyright 1999-2025 Gentoo Authors
+# Distributed under the terms of the GNU General Public License v2
+
+EAPI=8
+
+PYTHON_COMPAT=( python3_{11..14} )
+inherit cmake-multilib crossdev flag-o-matic llvm.org llvm-utils
+inherit python-any-r1 toolchain-funcs
+
+DESCRIPTION="C++ runtime stack unwinder from LLVM"
+HOMEPAGE="https://llvm.org/docs/ExceptionHandling.html"
+
+LICENSE="Apache-2.0-with-LLVM-exceptions || ( UoI-NCSA MIT )"
+SLOT="0"
+KEYWORDS="~amd64 ~arm ~arm64 ~loong ~mips ~ppc ~ppc64 ~riscv ~sparc ~x86 ~arm64-macos ~x64-macos"
+IUSE="+clang debug static-libs test"
+REQUIRED_USE="test? ( clang )"
+RESTRICT="!test? ( test )"
+
+RDEPEND="
+	!sys-libs/libunwind
+"
+DEPEND="
+	llvm-core/llvm:${LLVM_MAJOR}
+"
+BDEPEND="
+	clang? (
+		llvm-core/clang:${LLVM_MAJOR}
+		llvm-core/clang-linker-config:${LLVM_MAJOR}
+		llvm-runtimes/clang-rtlib-config:${LLVM_MAJOR}
+	)
+	!test? (
+		${PYTHON_DEPS}
+	)
+	test? (
+		$(python_gen_any_dep 'dev-python/lit[${PYTHON_USEDEP}]')
+	)
+"
+
+LLVM_COMPONENTS=( runtimes libunwind libcxx llvm/cmake cmake )
+LLVM_TEST_COMPONENTS=( libc libcxxabi llvm/utils/llvm-lit )
+llvm.org_set_globals
+
+python_check_deps() {
+	use test || return 0
+	python_has_version "dev-python/lit[${PYTHON_USEDEP}]"
+}
+
+test_compiler() {
+	target_is_not_host && return
+	local compiler=${1}
+	shift
+	${compiler} ${CFLAGS} ${LDFLAGS} "${@}" -o /dev/null -x c - \
+		<<<'int main() { return 0; }' &>/dev/null
+}
+
+multilib_src_configure() {
+	if use clang; then
+		llvm_prepend_path -b "${LLVM_MAJOR}"
+	fi
+
+	local libdir=$(get_libdir)
+
+	# https://github.com/llvm/llvm-project/issues/56825
+	# also separately bug #863917
+	filter-lto
+
+	# Workaround for bgo #961153.
+	# TODO: Fix the multilib.eclass, so it sets CTARGET properly.
+	if ! is_crosspkg; then
+		export CTARGET=${CHOST}
+	fi
+
+	if use clang; then
+		local -x CC=${CTARGET}-clang-${LLVM_MAJOR}
+		local -x CXX=${CTARGET}-clang++-${LLVM_MAJOR}
+		strip-unsupported-flags
+
+		# The full clang configuration might not be ready yet. Use the partial
+		# configuration files that are guaranteed to exist even during initial
+		# installations and upgrades.
+		local flags=(
+			--config="${ESYSROOT}"/etc/clang/"${LLVM_MAJOR}"/gentoo-{rtlib,linker}.cfg
+		)
+		local -x CFLAGS="${CFLAGS} ${flags[@]}"
+		local -x CXXFLAGS="${CXXFLAGS} ${flags[@]}"
+		local -x LDFLAGS="${LDFLAGS} ${flags[@]}"
+	fi
+
+	# Check whether C compiler runtime is available.
+	if ! test_compiler "$(tc-getCC)"; then
+		local nolib_flags=( -nodefaultlibs -lc )
+		if test_compiler "$(tc-getCC)" "${nolib_flags[@]}"; then
+			local -x LDFLAGS="${LDFLAGS} ${nolib_flags[*]}"
+			ewarn "${CC} seems to lack runtime, trying with ${nolib_flags[*]}"
+		elif test_compiler "$(tc-getCC)" "${nolib_flags[@]}" -nostartfiles; then
+			# Avoiding -nostartfiles earlier on for bug #862540,
+			# and set available entry symbol for bug #862798.
+			nolib_flags+=( -nostartfiles -e main )
+			local -x LDFLAGS="${LDFLAGS} ${nolib_flags[*]}"
+			ewarn "${CC} seems to lack runtime, trying with ${nolib_flags[*]}"
+		fi
+	fi
+	# Check whether C++ standard library is available,
+	local nostdlib_flags=( -nostdlib++ )
+	if ! test_compiler "$(tc-getCXX)" &&
+		test_compiler "$(tc-getCXX)" "${nostdlib_flags[@]}"
+	then
+		local -x LDFLAGS="${LDFLAGS} ${nostdlib_flags[*]}"
+		ewarn "${CXX} seems to lack runtime, trying with ${nostdlib_flags[*]}"
+	fi
+
+	# link to compiler-rt
+	# https://github.com/gentoo/gentoo/pull/21516
+	local use_compiler_rt=OFF
+	[[ $(tc-get-c-rtlib) == compiler-rt ]] && use_compiler_rt=ON
+
+	# Respect upstream build type assumptions (bug #910436) where they do:
+	# -DLIBUNWIND_ENABLE_ASSERTIONS=ON =>
+	#       -DCMAKE_BUILD_TYPE=DEBUG  => -UNDEBUG
+	#       -DCMAKE_BUILD_TYPE!=debug => -DNDEBUG
+	# -DLIBUNWIND_ENABLE_ASSERTIONS=OFF =>
+	#       -UNDEBUG
+	# See also https://github.com/llvm/llvm-project/issues/86#issuecomment-1649668826.
+	use debug || append-cppflags -DNDEBUG
+
+	local mycmakeargs=(
+		-DLLVM_ROOT="${ESYSROOT}/usr/lib/llvm/${LLVM_MAJOR}"
+
+		-DCMAKE_C_COMPILER_TARGET="${CTARGET}"
+		-DCMAKE_CXX_COMPILER_TARGET="${CTARGET}"
+		-DPython3_EXECUTABLE="${PYTHON}"
+		-DLLVM_ENABLE_RUNTIMES="libunwind"
+		-DLLVM_LIBDIR_SUFFIX=${libdir#lib}
+		-DLLVM_INCLUDE_TESTS=OFF
+		-DLIBUNWIND_ENABLE_ASSERTIONS=$(usex debug)
+		-DLIBUNWIND_ENABLE_STATIC=$(usex static-libs)
+		-DLIBUNWIND_INCLUDE_TESTS=$(usex test)
+		-DLIBUNWIND_INSTALL_HEADERS=ON
+
+		# cross-unwinding increases unwinding footprint (to account
+		# for the worst case) and causes some breakage on AArch64
+		# https://github.com/llvm/llvm-project/issues/152549
+		-DLIBUNWIND_ENABLE_CROSS_UNWINDING=OFF
+
+		# avoid dependency on libgcc_s if compiler-rt is used
+		-DLIBUNWIND_USE_COMPILER_RT=${use_compiler_rt}
+	)
+	if is_crosspkg; then
+		mycmakeargs+=(
+			# Without this, the compiler will compile a test program
+			# and fail due to no builtins.
+			-DCMAKE_C_COMPILER_WORKS=1
+			-DCMAKE_CXX_COMPILER_WORKS=1
+			# Install inside the cross sysroot.
+			-DCMAKE_INSTALL_PREFIX="${EPREFIX}/usr/${CTARGET}/usr"
+		)
+	fi
+	if use test; then
+		mycmakeargs+=(
+			-DLLVM_ENABLE_RUNTIMES="libunwind;libcxxabi;libcxx"
+			-DLLVM_EXTERNAL_LIT="${EPREFIX}/usr/bin/lit"
+			-DLLVM_LIT_ARGS="$(get_lit_flags)"
+			-DLIBUNWIND_LIBCXX_PATH="${WORKDIR}/libcxx"
+
+			-DLIBCXXABI_LIBDIR_SUFFIX=
+			-DLIBCXXABI_ENABLE_SHARED=OFF
+			-DLIBCXXABI_ENABLE_STATIC=ON
+			-DLIBCXXABI_USE_LLVM_UNWINDER=ON
+			-DLIBCXXABI_INCLUDE_TESTS=OFF
+
+			-DLIBCXX_LIBDIR_SUFFIX=
+			-DLIBCXX_ENABLE_SHARED=OFF
+			-DLIBCXX_ENABLE_STATIC=ON
+			-DLIBCXX_CXX_ABI=libcxxabi
+			-DLIBCXX_ENABLE_ABI_LINKER_SCRIPT=OFF
+			-DLIBCXX_HAS_MUSL_LIBC=$(llvm_cmake_use_musl)
+			-DLIBCXX_HAS_GCC_S_LIB=OFF
+			-DLIBCXX_INCLUDE_TESTS=OFF
+			-DLIBCXX_INCLUDE_BENCHMARKS=OFF
+		)
+	fi
+
+	cmake_src_configure
+}
+
+multilib_src_test() {
+	local -x LIT_PRESERVES_TMP=1
+	cmake_build check-unwind
+}
+
+multilib_src_install() {
+	DESTDIR=${D} cmake_build install-unwind
+}
--- a/llvm-runtimes/libunwind/libunwind-22.0.0.9999.ebuild
+++ b/llvm-runtimes/libunwind/libunwind-22.0.0.9999.ebuild
@ -25,6 +25,8 @@ DEPEND="
 BDEPEND="
 	clang? (
 		llvm-core/clang:${LLVM_MAJOR}
+		llvm-core/clang-linker-config:${LLVM_MAJOR}
+		llvm-runtimes/clang-rtlib-config:${LLVM_MAJOR}
 	)
 	!test? (
 		${PYTHON_DEPS}
@ -43,6 +45,14 @@ python_check_deps() {
 	python_has_version "dev-python/lit[${PYTHON_USEDEP}]"
 }

+test_compiler() {
+	target_is_not_host && return
+	local compiler=${1}
+	shift
+	${compiler} ${CFLAGS} ${LDFLAGS} "${@}" -o /dev/null -x c - \
+		<<<'int main() { return 0; }' &>/dev/null
+}
+
 multilib_src_configure() {
 	if use clang; then
 		llvm_prepend_path -b "${LLVM_MAJOR}"
@ -61,9 +71,42 @@ multilib_src_configure() {
 	fi

 	if use clang; then
-		local -x CC=${CTARGET}-clang
-		local -x CXX=${CTARGET}-clang++
+		local -x CC=${CTARGET}-clang-${LLVM_MAJOR}
+		local -x CXX=${CTARGET}-clang++-${LLVM_MAJOR}
 		strip-unsupported-flags
+
+		# The full clang configuration might not be ready yet. Use the partial
+		# configuration files that are guaranteed to exist even during initial
+		# installations and upgrades.
+		local flags=(
+			--config="${ESYSROOT}"/etc/clang/"${LLVM_MAJOR}"/gentoo-{rtlib,linker}.cfg
+		)
+		local -x CFLAGS="${CFLAGS} ${flags[@]}"
+		local -x CXXFLAGS="${CXXFLAGS} ${flags[@]}"
+		local -x LDFLAGS="${LDFLAGS} ${flags[@]}"
+	fi
+
+	# Check whether C compiler runtime is available.
+	if ! test_compiler "$(tc-getCC)"; then
+		local nolib_flags=( -nodefaultlibs -lc )
+		if test_compiler "$(tc-getCC)" "${nolib_flags[@]}"; then
+			local -x LDFLAGS="${LDFLAGS} ${nolib_flags[*]}"
+			ewarn "${CC} seems to lack runtime, trying with ${nolib_flags[*]}"
+		elif test_compiler "$(tc-getCC)" "${nolib_flags[@]}" -nostartfiles; then
+			# Avoiding -nostartfiles earlier on for bug #862540,
+			# and set available entry symbol for bug #862798.
+			nolib_flags+=( -nostartfiles -e main )
+			local -x LDFLAGS="${LDFLAGS} ${nolib_flags[*]}"
+			ewarn "${CC} seems to lack runtime, trying with ${nolib_flags[*]}"
+		fi
+	fi
+	# Check whether C++ standard library is available,
+	local nostdlib_flags=( -nostdlib++ )
+	if ! test_compiler "$(tc-getCXX)" &&
+		test_compiler "$(tc-getCXX)" "${nostdlib_flags[@]}"
+	then
+		local -x LDFLAGS="${LDFLAGS} ${nostdlib_flags[*]}"
+		ewarn "${CXX} seems to lack runtime, trying with ${nostdlib_flags[*]}"
 	fi

 	# link to compiler-rt
--- a/llvm-runtimes/libunwind/libunwind-22.0.0_pre20250831.ebuild
+++ b/llvm-runtimes/libunwind/libunwind-22.0.0_pre20250831.ebuild
@ -25,6 +25,8 @@ DEPEND="
 BDEPEND="
 	clang? (
 		llvm-core/clang:${LLVM_MAJOR}
+		llvm-core/clang-linker-config:${LLVM_MAJOR}
+		llvm-runtimes/clang-rtlib-config:${LLVM_MAJOR}
 	)
 	!test? (
 		${PYTHON_DEPS}
@ -43,6 +45,14 @@ python_check_deps() {
 	python_has_version "dev-python/lit[${PYTHON_USEDEP}]"
 }

+test_compiler() {
+	target_is_not_host && return
+	local compiler=${1}
+	shift
+	${compiler} ${CFLAGS} ${LDFLAGS} "${@}" -o /dev/null -x c - \
+		<<<'int main() { return 0; }' &>/dev/null
+}
+
 multilib_src_configure() {
 	if use clang; then
 		llvm_prepend_path -b "${LLVM_MAJOR}"
@ -61,9 +71,42 @@ multilib_src_configure() {
 	fi

 	if use clang; then
-		local -x CC=${CTARGET}-clang
-		local -x CXX=${CTARGET}-clang++
+		local -x CC=${CTARGET}-clang-${LLVM_MAJOR}
+		local -x CXX=${CTARGET}-clang++-${LLVM_MAJOR}
 		strip-unsupported-flags
+
+		# The full clang configuration might not be ready yet. Use the partial
+		# configuration files that are guaranteed to exist even during initial
+		# installations and upgrades.
+		local flags=(
+			--config="${ESYSROOT}"/etc/clang/"${LLVM_MAJOR}"/gentoo-{rtlib,linker}.cfg
+		)
+		local -x CFLAGS="${CFLAGS} ${flags[@]}"
+		local -x CXXFLAGS="${CXXFLAGS} ${flags[@]}"
+		local -x LDFLAGS="${LDFLAGS} ${flags[@]}"
+	fi
+
+	# Check whether C compiler runtime is available.
+	if ! test_compiler "$(tc-getCC)"; then
+		local nolib_flags=( -nodefaultlibs -lc )
+		if test_compiler "$(tc-getCC)" "${nolib_flags[@]}"; then
+			local -x LDFLAGS="${LDFLAGS} ${nolib_flags[*]}"
+			ewarn "${CC} seems to lack runtime, trying with ${nolib_flags[*]}"
+		elif test_compiler "$(tc-getCC)" "${nolib_flags[@]}" -nostartfiles; then
+			# Avoiding -nostartfiles earlier on for bug #862540,
+			# and set available entry symbol for bug #862798.
+			nolib_flags+=( -nostartfiles -e main )
+			local -x LDFLAGS="${LDFLAGS} ${nolib_flags[*]}"
+			ewarn "${CC} seems to lack runtime, trying with ${nolib_flags[*]}"
+		fi
+	fi
+	# Check whether C++ standard library is available,
+	local nostdlib_flags=( -nostdlib++ )
+	if ! test_compiler "$(tc-getCXX)" &&
+		test_compiler "$(tc-getCXX)" "${nostdlib_flags[@]}"
+	then
+		local -x LDFLAGS="${LDFLAGS} ${nostdlib_flags[*]}"
+		ewarn "${CXX} seems to lack runtime, trying with ${nostdlib_flags[*]}"
 	fi

 	# link to compiler-rt