Skip tests that require `-gstructor-decl-linkage-names` on Clang versions that don't support it.
Don't pass `-gno-structor-decl-linkage-names` on Clang versions where it the flag didn't exist but it was the default behaviour of the compiler anyway.
Drive-by:
- We used to run `self.expect("Bar()")` which would always fail. So the `error=True` would be true even if we didn't pass the `-gno-structor-linkage-names`. So it wasn't testing the behaviour properly. This patch changes these to `self.expect("expr Bar()")`.
faf070f062