* x64: Deduplicate fcmp emission logic
The `select`-of-`fcmp` lowering duplicated a good deal of `FloatCC`
lowering logic that was already done by `emit_fcmp`, so this commit
refactors these lowering rules to instead delegate to `emit_fcmp` and
then handle that result.
* Swap order of condition codes
Shouldn't affect the correctness of this operation and it's a bit more
natural to write the lowering rule this way.
* Swap the order of comparison operands
No need to swap `a b`, only the `x y` needs swapping.
* Fix x64 printing of `XmmCmove`
afb417920d