Debug Info: for static member variables, always put AT_MIPS_linkage_name to the

definition DIE (TAG_variable), and put AT_MIPS_linkage_name to TAG_member when
DarwinGDBCompat is true.

Darwin GDB needs AT_MIPS_linkage_name at both places to work.

Follow-up patch to r176143.
rdar://problem/13291234

llvm-svn: 176220