Improve codegen for select's:

if (x != 0) x = 1
if (x == 1) x = 1

Previous codegen looks like this:
        mov     r1, r0
        cmp     r1, #1
        mov     r0, #0
        moveq   r0, #1

The naive lowering select between two different values. It should recognize the
test is equality test so it's more a conditional move rather than a select:
        cmp     r0, #1
        movne   r0, #0

rdar://9758317

llvm-svn: 135017