xcompile: Fix clang compiler runtime detection

clang, like gcc, needs a compiler runtime library. Unlike gcc, it can
use either its own runtime library (compiler-rt), or gcc's version
(libgcc). Also unlike gcc, the version of clang that is currently part
of our reference toolchain does not provide the necessary versions of
compiler-rt for all platforms we support. Hence, for now, use libgcc
even on clang builds.  This patch allows switching between the two, but
switching to compiler-rt will break clang builds, unless someone fixes
our reference toolchain to provide libclang_rt.builtins-${ARCH}.a for
each of our supported platforms.

Change-Id: I5001a4b62ed34df19312f980b927ced8cbaf07db
Signed-off-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-on: https://review.coreboot.org/20303
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martinroth@google.com>
1 file changed