[NFC][Codegen][X86][AArch64][ARM][PowerPC] Recommit: Add test coverage for...

[NFC][Codegen][X86][AArch64][ARM][PowerPC] Recommit: Add test coverage for "add-of-inc" vs "sub-of-not"

I initially committed it with --check-prefix instead of --check-prefixes
(again, shame on me, and utils/update_*.py not complaining!)
and did not have a moment to understand the failure,
so i reverted it initially in rL64939.

llvm-svn: 364945