[ubsan] nonnull and returns_nonnull sanitization

[Jakub Jelinek]

On Tue, Jul 29, 2014 at 07:43:33PM -0700, Alexey Samsonov wrote:
> Once again, sorry for the delay =/
> 
> I hope to get to this patch this/next week.

Would it be acceptable to just get the libubsan bits in right now
(either the patch I've posted, or some minor wording differences or whatever
you'd like to change) and get the clang side done when you find time for it?

	Jakub