Fix diagnostic test to tolerate Clang diagnosing it as well.

Tuple has tests that ensure we diagnose non-lifetime extended
reference bindings inside tuples constructors. As of yesterday,
Clang now does this for us.

Adjust the test to tolerate the new diagnostics, while still
testing that we emit diagnostics of our own. Maybe after this
version of Clang has been adopted by most users we should
remove our diagnostics; but for now more error detection is
better!

llvm-svn: 337905