[X86] Fold (movmsk (setne (and X, (1 << C)), 0)) -> (movmsk (X << C))

Summary:
MOVMSK only care about the sign bit so we don't need the setcc to fill the whole element with 0s/1s. We can just shift the bit we're looking for into the sign bit. This saves a constant pool load.

Inspired by PR38840.

Reviewers: RKSimon, spatel

Reviewed By: RKSimon

Subscribers: lebedev.ri, llvm-commits

Differential Revision: https://reviews.llvm.org/D52121

llvm-svn: 342326