sys-devel/clang: stop setting GCC_INSTALL_PREFIX for prefix

Clang 19 deprecates the GCC_INSTALL_PREFIX CMake option.

We now handle this via config files installed by gcc-config. If there's
any remaining issues for Prefix, it should be handled over there
or in sys-devel/clang-common.

Closes: https://bugs.gentoo.org/939816
Signed-off-by: Sam James <sam@gentoo.org>

sys-devel/clang/clang-19.1.0.ebuild

@@ -331,12 +331,6 @@ multilib_src_configure() {
 		)
 	fi
 
-	if [[ -n ${EPREFIX} ]]; then
-		mycmakeargs+=(
-			-DGCC_INSTALL_PREFIX="${EPREFIX}/usr"
-		)
-	fi
-
 	if tc-is-cross-compiler; then
 		has_version -b sys-devel/clang:${LLVM_MAJOR} ||
 			die "sys-devel/clang:${LLVM_MAJOR} is required on the build host."

sys-devel/clang/clang-20.0.0.9999.ebuild

@@ -329,12 +329,6 @@ multilib_src_configure() {
 		)
 	fi
 
-	if [[ -n ${EPREFIX} ]]; then
-		mycmakeargs+=(
-			-DGCC_INSTALL_PREFIX="${EPREFIX}/usr"
-		)
-	fi
-
 	if tc-is-cross-compiler; then
 		has_version -b sys-devel/clang:${LLVM_MAJOR} ||
 			die "sys-devel/clang:${LLVM_MAJOR} is required on the build host."

sys-devel/clang/clang-20.0.0_pre20240917.ebuild

@@ -331,12 +331,6 @@ multilib_src_configure() {
 		)
 	fi
 
-	if [[ -n ${EPREFIX} ]]; then
-		mycmakeargs+=(
-			-DGCC_INSTALL_PREFIX="${EPREFIX}/usr"
-		)
-	fi
-
 	if tc-is-cross-compiler; then
 		has_version -b sys-devel/clang:${LLVM_MAJOR} ||
 			die "sys-devel/clang:${LLVM_MAJOR} is required on the build host."

sys-devel/clang/clang-20.0.0_pre20240924.ebuild

@@ -332,12 +332,6 @@ multilib_src_configure() {
 		)
 	fi
 
-	if [[ -n ${EPREFIX} ]]; then
-		mycmakeargs+=(
-			-DGCC_INSTALL_PREFIX="${EPREFIX}/usr"
-		)
-	fi
-
 	if tc-is-cross-compiler; then
 		has_version -b sys-devel/clang:${LLVM_MAJOR} ||
 			die "sys-devel/clang:${LLVM_MAJOR} is required on the build host."