[PATCH] Let "-w" ignore all warnings

[Jordan Rose]

  I think my point was that a diagnostic that is DefaultError is not a "warning" but an "error that can be turned off". Most are DefaultErrors because the code is invalid: even if the compiler can do something with it, it's probably still a bad idea (such as delegating constructor cycles or returning something in a void method). I wouldn't want those to go away when I add -w. But I may be in the minority here.

  FWIW, I'd be perfectly happy to say that -Wstatic-float-init should be an ExtWarn instead of a DefaultError, or that it's only a DefaultError in C++11 mode where there's an alternative.

http://llvm-reviews.chandlerc.com/D551