This adds the argument --dump-ir to clang-import-test, which allows viewing of the final IR. This is useful for confirming that structure layout was correct.
I've added an XFAILed test that exercises this, checking that a struct defined inside a function body has the right fields. Currently it does not because LookupSameContext() (ExternalASTMerger.cpp) can't find the struct. This is an issue I intend to resolve separately.