COFF Import: expose both symbols

COFF Import libraries which use the obsolete CONSTANT export are
supposed to get two symbols, one with the `_imp_` prefix and one
without.  Ensure that we expose both for iteration.  This is necessary
to fix the librarian with COFF CONSTANT exports.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@301614 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed