Merging r196970:

------------------------------------------------------------------------
r196970 | fang | 2013-12-10 16:37:41 -0500 (Tue, 10 Dec 2013) | 3 lines

on darwin<10, fallback to .weak_definition (PPC,X86)
.weak_def_can_be_hidden was not yet supported by the system assembler

------------------------------------------------------------------------

llvm-svn: 206050