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

[reed kotler]

In the constructor for mips fast isel is the following line of code:

    TargetSupported = ((Subtarget->getRelocationModel() == Reloc::PIC_) &&
                       (Subtarget->hasMips32r2() && (Subtarget->isABI_O32())));

If TargetSupported is false then we don't do Mips fast isel, even if it is requested.

http://reviews.llvm.org/D4827