powerpc: enable supported sanitizers on powerpc64*
- Merge LLVM's 315d792130258a9b7250494be8d002ebb427b08f, adding support
for FreeBSD/powerpc64*.
- Add sanitizer list to lib/libclang_rt/Makefile, taken from the list of
libraries that llvm-devel port builds.
- powerpc64le supports the same sanitizers that powerpc64, but powerpc64le
also supports xray* sanitizers.
- lib/libclang_rt/xray/Makefile hardcodes amd64-specific files, so that needs
to be conditionalized.
- Sanitizers are not enabled for powerpc, because powerpc supports only
builtins and profile.
Reviewed by: dim
Differential Revision: https://reviews.freebsd.org/D35228
Relnotes: yes
MFC after: 3 days