Undefine HAVE_(DE)REGISTER_FRAME in llvm's config.h on arm

Otherwise, the lli tool (enable by WITH_CLANG_EXTRAS) won't link on arm,
stating that __register_frame is undefined. This function is normally
provided by libunwind, but explicitly not for the ARM Exception ABI.

Reported by: oh
PR: 255570
MFC after: 6 weeks

(cherry picked from commit f336b45e943c7f9a90ffcea1a6c4c7039e54c73c)