Added inst combine transforms for single bit tests from Chris's note

if ((x & C) == 0) x |= C becomes x |= C

if ((x & C) != 0) x ^= C becomes x &= ~C

if ((x & C) == 0) x ^= C becomes x |= C

if ((x & C) != 0) x &= ~C becomes x &= ~C

if ((x & C) == 0) x &= ~C becomes nothing

Z3 Verifications code for above transform

http://rise4fun.com/Z3/Pmsh

Differential Revision: http://reviews.llvm.org/D3717