[libc++abi][AIX] add personality and helper functions for the state table EH

This patch adds the personality and helper functions for the state table based EH used by IBM legacy compilers xlC and xlclang++ on AIX.

 * A high level description of the state table based EH is provided in the code comments.

 * Function scan_state_tab() is added to scan the state table. It is invoked by the state table personality routine __xlcxx_personality_v0() and returns scan_results like scan_eh_tab() does.

 * A couple of EH helper functions used by xlC and xlclang++ generated code are also added, e.g., __xlc_catch_matchv2() which checks whether the thrown object matches the catch handler's exception type.

 * Debugging macros _LIBCXXABI_TRACE_STATETAB, _LIBCXXABI_TRACE_STATETAB0, and _LIBCXXABI_TRACING_STATETAB are added to dump state table scanning traces if environment variable LIBCXXABI_PRINT_STATTAB is set.

 * The state variable and state table data is the LSDA found from the traceback table of the function during unwinding.

Reviewed by: MaskRay, cebowleratibm, libc++abi

Differential Revision: https://reviews.llvm.org/D100504

GitOrigin-RevId: b8f5732634feaf7a9ce37d33f97f1fb490efeddd
2 files changed