Make libatomic_ops buildable and enable on non-X86.

Change-Id: Iec1d329f143ab76de7e8b4acd3da66efb6e0220c
Reviewed-on: https://gerrit.libreoffice.org/5812
Reviewed-by: Andrzej J.R. Hunt <andrzej@ahunt.org>
Tested-by: Andrzej J.R. Hunt <andrzej@ahunt.org>
Reviewed-on: https://gerrit.libreoffice.org/6600