Special case simple binary operator X op C

Special case simple binary operator X op C

  This avoid generating a register to hold C, which in turn speeds up the
  register allocator by a lot: ~9% on 164.gzip and ~17% on 256.bzip2.  This
  also speeds up other passes.  This also speeds up execution of the program
  marginally, and makes the asm much easier to read. :)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@6626 91177308-0d34-0410-b5e6-96231b3b80d8