[x86] use SETCC_CARRY instead of SBB node for select lowering

This is a suggested follow-up to D116765.
This removes a clear of the register operand, so it is better
for code size, but it does potentially create a false register
dependency on surrounding code. If that is a problem, it should
be solvable using dependency-breaking code that is used for
other instructions.

Differential Revision: https://reviews.llvm.org/D116804