swift234

[Driver] Rebuild everything when command-line arguments change.

If certain command-line arguments change, the results of the last
compilation aren't reusable, i.e. we can't do an incremental build.
Do a full rebuild when we detect that this happens.

(Which command-line options? Conservatively assume all of them, /except/
those with the new DoesNotAffectIncrementalBuild flag in Options.td.)

Swift SVN r24385