This removes the dependency on the llvm mangler doing it for us. In isolation,
the benefit is that the testing of what mangling is applied is all in one place:
(C, C++) X (Itanium, Microsoft) are all handled by clang.
This also gives me hope that in the future the llvm mangler (and llvm-ar) will
not depend on TargetMachine.
llvm-svn: 192762
Rafael Espindola