libunwind: Fix build race conflict with gcc and musl
Building libunwind, then gcc-runtime causes build failures. This is hard
to fix since gcc-runtime wants the internal gcc unwind.h header but libunwind
wants to provide this. There are differences in include behaviour between gcc
and glibc which are by design.
This patch hacks around the issue by looking for a define used during gcc-runtime's
build and skipping to the internal header in that case. The patch is only enabled
on musl and is the best workaround I could come up with to unblock failing builds
on our autobuilder.
[YOCTO #10129]
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
