X86: Bad peephole interaction between adc, MOV32r0

The peephole tries to reorder MOV32r0 instructions such that they are
before the instruction that modifies EFLAGS.

The problem is that the peephole does not consider the case where the
instruction that modifies EFLAGS also depends on the previous state of
EFLAGS.

Instead, walk backwards until we find an instruction that has a def for
EFLAGS but does not have a use.
If we find such an instruction, insert the MOV32r0 before it.
If it cannot find such an instruction, skip the optimization.