Jit64: divwx - Eliminate XOR for constant dividend

We normally check for division by zero to know if we should set the
destination register to zero with a XOR. However, when the divisor and
destination registers are the same the explicit zeroing can be omitted.
In addition, some of the surrounding branching can be simplified as
well.

Before:
45 85 FF             test        r15d,r15d
75 05                jne         normal_path
45 33 FF             xor         r15d,r15d
EB 0C                jmp         done
normal_path:
B8 5A 00 00 00       mov         eax,5Ah
99                   cdq
41 F7 FF             idiv        eax,r15d
44 8B F8             mov         r15d,eax
done:

After:
45 85 FF             test        r15d,r15d
74 0C                je          done
B8 5A 00 00 00       mov         eax,5Ah
99                   cdq
41 F7 FF             idiv        eax,r15d
44 8B F8             mov         r15d,eax
done:

0 files changed, 0 insertions, 0 deletions