[X86] Handle SETB_C32r/SETB_C64r in flag copy lowering the same way we handle SBB

Previously we took the restored flag in a GPR, extended it 32 or 64 bits. Then used as an input to a sub from 0. This requires creating a zero extend and creating a 0.

This patch changes this to just use an ADD with 255 to restore the carry flag and keep the SETB_C32r/SETB_C64r. Exactly like we handle SBB which is what SETB becomes.

Differential Revision: https://reviews.llvm.org/D74152