ENH: robustness, consistency for wmake -show-api, -version

- add to wmakeFunctions to ensure it works even without 'make' being
  installed. Exit immediately after -show-api for consistency with
  -version.

foamEtcFile:
  - drop warnings for some old (pre-v1812) defunct options
    and simply flag as unknown options.
  - handle -version, --version as equivalent to -show-api