Verifier: Ignore CUs pulled in by ODR-uniqued types.

When more than one Module is imported into the same context, such as during
an LTO build before linking the modules, ODR type uniquing may cause types
to point to a different CU. This check does not make sense in this case.

This fixes the error reported in PR34944.

https://bugs.llvm.org/show_bug.cgi?id=34944
rdar://problem/34940685

This reapplies a cleaner implementation of r316049.

llvm-svn: 316052