Relax an assert a bit to avoid a crash on unreachable code.

Patch by Duncan Exon Smith with a small tweak by me.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222984 91177308-0d34-0410-b5e6-96231b3b80d8
Add a test showing what the linker IdentifiedStructTypes is for.

Without this it could just be deleted and all tests would pass.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222985 91177308-0d34-0410-b5e6-96231b3b80d8