Simplify add-with-overflow pattern (uaddo)

[chfast]

For unsigned integers to check if an addition overflowed (get carry bit) it is enough to compare the sum with one of its arguments carry = sum < a. However, it is not obvious that it is enough to only check one of the arguments and we may encounter a pattern where both arguments are checked.

define i1 @src(i64 %a, i64 %b){
  %s = add i64 %a, %b
  %cond_a = icmp ult i64 %s, %a
  %cond_b = icmp ult i64 %s, %b
  %cond = or i1 %cond_a, %cond_b
  ret i1 %cond
}

define i1 @tgt(i64 %a, i64 %b){
  %s = add i64 %a, %b
  %cond_a = icmp ult i64 %s, %a
  ret i1 %cond_a
}

Playground: https://godbolt.org/z/TW8enc6zo
Proof: https://alive2.llvm.org/ce/z/iPAE7t