Fix typo in PPCInstr64Bit
Cleanup PPC CR-spill kill flags and 32- vs. 64-bit instructions

There were a few places where kill flags were not being set correctly, and
where 32-bit instruction variants were being used with 64-bit registers. After
r178180, this code was being triggered causing llc to assert.
Disable JIT/MCJIT tests in unittests/ExecutionEngine for the targets that don't support JIT.