[COFF] Make it clearer that the symbols subsection holds function display name rather than just name

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221812 91177308-0d34-0410-b5e6-96231b3b80d8
Temporary fix for PR21528 - use mangled C++ function names in COFF debug info to un-break ASan on Windows

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221813 91177308-0d34-0410-b5e6-96231b3b80d8