Pass -gcodeview-ghash when using clang-cl and lld-link
This precomputes some hashes that LLD uses for type merging to speed up
linking when PDBs are enabled. Only do this if any kind of /DEBUG flag
is passed to the linker. -gcodeview-ghash is orthogonal to /Z7, -g, -g1,
or -gmlt, so it is safe to set it independently from those flags. It
will not increase debug info emission.
Differential Revision: https://reviews.llvm.org/D103287