[PATCH] [X86] Fix pattern match for 32-to-64-bit zext in the presence of AssertSext

[Michael Kuperstein]

AArch64 and MSP have very similar patterns in their TD files - I guess copied from x86 - so I suspect they have the same issue. 
I don't know if they actually have the same bug, and I don't have either the hardware or the familiarity with their ISA to patch them, even though the actual patch ought to look the same.

Anyway, if you have any potential reviewers in mind (other than Nadav who's already on the review), feel free to suggest.

http://reviews.llvm.org/D6128