c++filt: support COFF import thunks

The synthetic thunk for the import is prefixed with __imp_.  Attempt to
undecorate the names when they begin with the __imp_ prefix.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@298550 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed