mktables: Regenerate if called with different cmd line args

mktables: Regenerate if called with different cmd line args

mktables acts pretty much like its own Makefile.  This is because the
rules for regenerating are complicated and too hard to keep in sync in a
Makefile with new versions of Unicode.  mktables itself already has
enough intelligence to automatically update the rules when it gets
modified to account for new files from Unicode.

However, prior to this commit, it didn't keep track of the options it
was called with, thus it wouldn't necessarily run when those options
changed to affect the desired outputs.