If the CPSR is defined by a copy, then we don't want to merge it into an IT

If the CPSR is defined by a copy, then we don't want to merge it into an IT
block. E.g., if we have:

  movs  r1, r1
  rsb   r1, 0
  movs  r2, r2
  rsb   r2, 0

we don't want this to be converted to:

  movs  r1, r1
  movs  r2, r2
  itt   mi
  rsb   r1, 0
  rsb   r2, 0

PR11107 & <rdar://problem/10259534>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@141589 91177308-0d34-0410-b5e6-96231b3b80d8