Added atomic_cmpxchg instruction
Added atomic_cmpxchg instruction

mpflanzer/Oclgrind,surround-io/oclgrind,surround-io/oclgrind,surround-io/oclgrind,surround-io/oclgrind,mpflanzer/Oclgrind,mpflanzer/Oclgrind,mpflanzer/Oclgrind