Would it make sense to have `dmd -v=json` to avoid custom parsing of -v ?
benefit:
* avoid having to maintain parsers for -v output (eg used in rdmd)
* current parser not forward/backward compatible with different dmd
releases (eg each time something is added, it can break the parser, eg
2.073 introduced `predefs   DigitalMars Posix OSX ..`
* useable in tooling
* avoid corner cases (eg escaping spaces etc)