[X86] Don't allow optimizeCompareInstr to replace a CMP with BEXTR if the sign flag is used.

The BEXTR instruction documents the SF bit as undefined.

The TBM BEXTR instruction has the same issue, but I'm not sure how to test it. With the control being an immediate we can determine the sign bit is 0 or the BEXTR would have been removed.

Fixes PR40060

Differential Revision: https://reviews.llvm.org/D55807

llvm-svn: 349956