[ARM] Lower lower saturate to 0 and lower saturate to -1 using bit-operations

Summary:
Expressions of the form x < 0 ? 0 :  x; and x < -1 ? -1 : x can be lowered using bit-operations instead of branching or conditional moves

In thumb-mode this results in a two-instruction sequence, a shift followed by a bic or or while in ARM/thumb2 mode that has flexible second operand the shift can be folded into a single bic/or instructions. In most cases this results in smaller code and possibly less branches, and in no case larger than before.

Patch by Marten Svanfeldt.

Reviewers: fhahn, pbarrio

Reviewed By: pbarrio

Subscribers: efriedma, rogfer01, aemerson, javed.absar, kristof.beyls, llvm-commits

Differential Revision: https://reviews.llvm.org/D42574

llvm-svn: 323869