Yay for Clang

So you write something new instead. Either way the onus is on you to convince other folks that your fork/new design/whatever is "better" than what was there before. Or use something else entirely. Meanwhile, assuming both old and new are F/OSS, farnz's point about not being able to "stifle competition through market power" equally applies, because you're always free [1] to do your own thing.

[1] As in, have the legal ability. As opposed to other practical "have the skills/time/money/etc".