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


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@176220 91177308-0d34-0410-b5e6-96231b3b80d8