Fix a crasher where when we're attempting to replace a type
during the finalization for CGDebugInfo in clang we would RAUW
a type and it would result in a corrupted MDNode for an
imported declaration.

Testcase pending as reducing has been difficult.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202540 91177308-0d34-0410-b5e6-96231b3b80d8
80-col.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202541 91177308-0d34-0410-b5e6-96231b3b80d8