[XCOFF][AIX] Generate LSDA data and compact unwind section on AIX
AIX uses the existing EH infrastructure in clang and llvm.
The major differences would be
- AIX do not have CFI instructions.
- AIX uses a new personality routine, named __xlcxx_personality_v1. It doesn't use the GCC personality rountine, because the interoperability is not there yet on AIX.
- AIX do not use eh_frame sections. Instead, it would use a eh_info
section (compat unwind section) to store the information about
personality routine and LSDA data address.
Reviewed By: daltenty, hubert.reinterpretcast
Differential Revision: https://reviews.llvm.org/D91455