[LLVMdev] DW_AT_[MIPS_]linkage_name inconsistency

[Robinson, Paul]

We're inconsistent about using DW_AT_MIPS_linkage_name versus
DW_AT_linkage_name.

Variables (see DwarfCompileUnit::getOrCreateGlobalVariableDIE())
get the standard attribute for DWARF >= 4, MIPS for older.

Subprograms (see DwarfUnit::applySubprogramDefinitionAttributes())
always get DW_AT_MIPS_linkage_name (no version check).

Before I go drudging through however many tests will die if I add
a version check... we DO want to fix this, right?
Thanks,
--paulr

P.S.  PS4 doesn't want linkage names at all, which will probably
be even more painful test-wise, but it seemed like cleaning up
this bit should come first regardless.