llvm/test/Transforms/GCOVProfiling: Avoid to parse backslashes in MDString. Use %/T instead of %T.

LLVM Parser decodes "\bb" as hex in "C:\bb-win7\buildername\build...", with MDString.

See also, http://llvm.org/docs/LangRef.html#metadata-nodes-and-metadata-strings

This reverts r221270, "Disable 3 tests in llvm/test/Transforms/GCOVProfiling/ for now. Investigating."

FIXME: Please check EC in GCOVProfiler::emitProfileNotes().

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221334 91177308-0d34-0410-b5e6-96231b3b80d8