Fix diagnostics where _Atomic can't be applied
adb290d97482aa9311ee4b4b5917a0f2ece55b30 added a new case to
err_atomic_specifier_bad_type. The diagnostic has two %select's
controlled by the same argument, but only the first was updated to have
the new case. Add the extra case for the second %select and add a
test case that exercises the last case.