app-containers/docker-cli: Fix cross-compiling man pages

This is done by rebuilding for the build system. These can be generated
as the target system using -exec, but this can still trigger rebuilds,
so it can be slower in practise.

Also drop CGO_CFLAGS/CGO_LDFLAGS handling as this isn't needed anymore.

Closes: https://bugs.gentoo.org/967481
Signed-off-by: James Le Cuirot <chewi@gentoo.org>

app-containers/docker-cli/docker-cli-29.1.3.ebuild

@@ -3,7 +3,7 @@
 
 EAPI=8
 
-inherit shell-completion go-module
+inherit shell-completion go-env go-module toolchain-funcs
 MY_PV=${PV/_/-}
 
 # update this on every bump
@@ -20,6 +20,7 @@ KEYWORDS="~amd64 ~arm ~arm64 ~loong ~ppc64 ~riscv ~x86"
 IUSE="selinux"
 
 RDEPEND="selinux? ( sec-policy/selinux-docker )"
+BDEPEND="dev-go/go-md2man"
 
 RESTRICT="installsources strip test"
 
@@ -32,14 +33,14 @@ src_prepare() {
 
 src_compile() {
 	export DISABLE_WARN_OUTSIDE_CONTAINER=1
-	# setup CFLAGS and LDFLAGS for separate build target
-	# see https://github.com/tianon/docker-overlay/pull/10
-	CGO_CFLAGS+=" -I${ESYSROOT}/usr/include"
-	CGO_LDFLAGS+=" -L${ESYSROOT}/usr/$(get_libdir)"
-		emake \
-		VERSION="${PV}" \
-		GITCOMMIT="${GIT_COMMIT}" \
-		dynbinary manpages
+
+	myemakeargs=(
+		VERSION="${PV}"
+		GITCOMMIT="${GIT_COMMIT}"
+	)
+
+	emake "${myemakeargs[@]}" dynbinary
+	tc-env_build go-env_run emake "${myemakeargs[@]}" manpages
 }
 
 src_install() {