[InstCombine] Fold `(icmp eq/ne (zext i1 X) (sext i1 Y))`-> `(icmp eq/ne (or X, Y), 0)`

This comes up when adding two `bool` types in C/C++
```
    bool foo(bool a, bool b) {
        return a + b;
    }
    ...
    ->
    define i1 @foo(i1 %a, i1 %b) {
        %conv = zext i1 %a to i32
        %conv3.neg = sext i1 %b to i32
        %tobool4 = icmp ne i32 %conv, %conv3.neg
        ret i1 %tobool4
}
```

Proof: https://alive2.llvm.org/ce/z/HffWAN

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D154574