[flang] Merge pull request flang-compiler/f18#531 from flang-compiler/pmk-more-fixes

Roll up more minor features & fixes to semantics for bugs found by regression testing

Original-commit: flang-compiler/f18@96a7932dab8247099d20e5e46bf9377666e424bd
Reviewed-on: https://github.com/flang-compiler/f18/pull/531