[Thumb] Select (CMPZ X, -C) -> (CMPZ (ADDS X, C), 0)

[Thumb] Select (CMPZ X, -C) -> (CMPZ (ADDS X, C), 0)

The CMPZ #0 disappears during peepholing, leaving just a tADDi3, tADDi8 or t2ADDri. This avoids having to materialize the expensive negative constant in Thumb-1, and allows a shrinking from a 32-bit CMN to a 16-bit ADDS in Thumb-2.

llvm-svn: 281040