Fix two remaining issue after fixing PR15355 when CMOV is not available

- Phi nodes should be replaced/updated after lowering CMOV into branch
  because 'mainMBB' updating operand in Phi node is changed.
- Add EFLAGS in livein before lowering the 2nd CMOV. It's necessary as
  we will reuse the EFLAGS generated before the 1st lowered CMOV, which
  won't clobber EFLAGS. However, we need explicitly specify that.
- '-attr=-cmov' test case are added.