We need to produce a setcc instruction which has an 8-bit result.
This gets rid of a bunch of cases that were using the s1->s8/s16/s32/s64
handling in selectZExt.
I'm not very familiar with GlobalISel yet so I'm not yet sure
the best way to do things. I'd especially like feedback on the
best way to handle the currently split 32-bit and 64-bit mode
handling.
You'll have to do something explicitly to handle non-0 address space pointers eventually, but this is a good enough first step