Support standalone LLVM/Clang as crosscompiler

This change makes it possible to use Clang instead of GCC in
Crossdev. As LLVM is already able to target other architectures,
provided that LLVM_TARGETS is set accordingly, the only thing needed
to do is compile builtins (compiler-rt) for the target triple. Note
that compiler-rt needs libc headers to target when building, and in
turn linux-headers needs to be installed for Linux targets, so most
stages except binutils and GCC are still there.

Currently having both a GCC and LLVM Crossdev environment installed
for the same triple is not supported since many ebuilds just use
/usr/${CTARGET} as a hardcoded sysroot, but I plan adding support.

Note: by standalone I mean a pure LLVM toolchain not dependent on an
existing GCC toolchain.

Bug: https://bugs.gentoo.org/680652
Signed-off-by: Alfred Persson Forsberg <cat@catcream.org>
Closes: https://github.com/gentoo/crossdev/pull/10
Signed-off-by: Sam James <sam@gentoo.org>

1 files changed, 20 insertions, 0 deletions

diff --git a/wrappers/emerge-wrapper b/wrappers/emerge-wrapper
index 87dcb00..79c182e 100755
--- a/wrappers/emerge-wrapper
+++ b/wrappers/emerge-wrapper
@@ -87,6 +87,26 @@ cross_wrap_etc()
 		-e "s:__CBUILD__:${CBUILD}:g" \
 		"${confs[@]}"
 
+	if [[ "${LLVM}" == "yes" ]] ; then
+		cat <<-EOF >>${SYSROOT}/etc/portage/profile/make.defaults
+	AR=llvm-ar
+	AS=llvm-as
+	CC="${CHOST}-clang"
+	CROSS_COMPILE="${CHOST}-"
+	CXX="${CHOST}-clang++"
+	DLLTOOL=llvm-dlltool
+	HOSTCC="${CC:=clang}"
+	HOSTCXX="${CXX:=clang++}"
+	LD=ld.lld
+	LLVM=1
+	NM=llvm-nm
+	OBJCOPY=llvm-objcopy
+	RANLIB=llvm-ranlib
+	READELF=llvm-readelf
+	STRIP=llvm-strip
+	EOF
+	fi
+
 	return 0
 }