DebugInfo: Fix cross-CU references for scopes (and variables within those scopes) in abstract definitions of cross-CU inlined functions

Found by Adrian Prantl during post-commit review of r209335.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209498 91177308-0d34-0410-b5e6-96231b3b80d8