[llvm] [InstCombine] Fold comparison of adding two z/sext booleans (PR #67895)

[via llvm-commits]

elhewaty wrote:

@nikic  Just to make sure that I didn't miss something.
I should write tests for every comparisons operator against the constants(-2, -1, 0, 1, 2), right?
so (eq, ne, ugt, uge, ult, ule, sgt, sge, slt, sle)[10] * 5 = 50 tests.
and some tests for other numbers just for confirmation like 10, -5, .. etc

https://github.com/llvm/llvm-project/pull/67895