[PowerPC] Fix some missed optimization opportunities in combineSetCC

For both operands are bool, short, int, long, long long, add the following optimization.
1. 0-x == y --> x+y ==0
2. 0-x != y --> x+y != 0

Review: nemanjai
Differential Revision: https://reviews.llvm.org/D53360

llvm-svn: 345366