This is a preparation for D125804, which makes test_errors.py test
warnings the same way it already tests errors, i.e., assert that the
emitted and expected errors are identical. The following changes are
made to the test:
- Add the WARNING directive where warnings are expected.
- Remove -Werror in the RUN line. It does not serve much purpose here: with -Werror flang makes compilation fail in the presence of warnings, but warnings are still printed as warnings and not as errors. And I anyway find it better to test the warnings as warnings instead of promoting them and test both warnings and errors as errors.
- Update the header comment describing the test case, mostly in response to the removal of -Werror.
- Remove the reference to 'issue 458', referring to https://github.com/flang-compiler/f18/issues/458, from the header. I think the relevant reference here is to C1120 of the standard, and references to bug trackers from other projects (from before upstreaming) can be confusing.