[PATCH] Add sign/zero extend to mips fast-isel

[reed kotler]

This initial port is just mips32/r2, pic, O2 . I've added O0 as a requirement. Nothing else is part of what we are doing at this time.

Worrying about other combinations is for future work. Its out of scope at this time, IMO.

SOme of these things, had I know about them, might have made sense for me to do in this first go around but I've already done it this way and this is in the scope of the work and passes all of test-suite so I don't feel there is any need to be making more changes, do the testing, etc. to cases that are out of scope of my assigned work.

http://reviews.llvm.org/D4827