Since XLC only ever shipped on PowerPC AIX and Linux, it is not reasonable to
provide the compatibility macros on any target other than those two. This patch
restricts those macros to AIX/Linux.
Differential revision: https://reviews.llvm.org/D110213
Add builtin and intrinsic for `__addex`.
This patch is part of a series of patches to provide builtins for
compatibility with the XL compiler.
Reviewed By: stefanp, nemanjai, NeHuang
Differential Revision: https://reviews.llvm.org/D107002