[flang] Merge pull request flang-compiler/f18#200 from flang-compiler/pmk3

Add a test, a flag, a fix, and a parse tree visitor tweak.

Original-commit: flang-compiler/f18@5344ef9272f2f46702e96409c8d697b927542e20
Reviewed-on: https://github.com/flang-compiler/f18/pull/200