[Symbolize] Use the local MSVC C++ demangler instead of relying on dbghelp. NFC.

This allows making a couple llvm-symbolizer tests run in all
environments.

Differential Revision: https://reviews.llvm.org/D68133

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@375041 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed