Also tightened up the acceptable condition operand for these instructions
on MIPS-I to MIPS-III. Support for $fcc[1-7] was added in MIPS-IV. Prior
to that only $fcc0 is acceptable.
We currently don't optimize (BEQZ (NOT $a), $target) and similar. It's
probably best to do this in InstCombine.
Depends on D4111