[X86] Emit SBB instead of SETCC_CARRY from LowerSELECT. Break false dependency on the SBB input.

I'm hoping we can just replace SETCC_CARRY with SBB. This is another step towards that.

I've explicitly used zero as the input to the setcc to avoid a false dependency that we've had with the SETCC_CARRY. I changed one of the patterns that used NEG to instead use an explicit compare with 0 on the LHS. We needed the zero anyway to avoid the false dependency. The negate would clobber its input register. By using a CMP we can avoid that which could be useful.

Differential Revision: https://reviews.llvm.org/D55414

llvm-svn: 348959

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