Merge commit cde8f4c16 from llvm git (by me):

Merge commit cde8f4c16 from llvm git (by me):

  Move special va_list handling to kmp_os.h

  Instead of copying and pasting the same #ifdef expressions in
  multiple places, define a type and a pair of macros in kmp_os.h, to
  handle whether va_list is pointer-like or not:

  * kmp_va_list is the type to use for __kmp_fork_call()
  * kmp_va_deref() dereferences a va_list, if necessary
  * kmp_va_addr_of() takes the address of a va_list, if necessary

  Also add FreeBSD to the list of OSes that has a non pointer-like
  va_list. This can now be easily extended to other OSes too.

  Reviewed By: AndreyChurbanov

  Differential Revision: https://reviews.llvm.org/D86397

This should enable building of LLVM's OpenMP on AArch64. Addition to
share/mk will follow in a subsequent commit.

PR:		248864
MFC after:	2 weeks