[libc++][AIX] Initial patch to unblock the libc++ build on AIX

This path would unblock the build of libc++ library on AIX:
2. Use uselocale to actually take the locale setting
   into account.
3. extract_mtime and extract_atime mod needed for AIX. As stat
   structure on AIX uses internal structure st_timespec to store
   time for binary compatibility reason. So we need to convert it
   back to timespec here.
4. Do not build cxa_thread_atexit.cpp for libcxxabi on AIX.

Differential Revision: https://reviews.llvm.org/D97558

GitOrigin-RevId: 158026301b4842bb877fc8a6a444c348da6d9f3b
1 file changed