Resolve docs inconsistency with Overflow builtins

In 41 (Undefined Behavior) . 5 (Integer Overflow) . 3 (Builtin Overflow Functions), it is stated that

> These builtins return a bool of whether or not overflow occurred, as well as returning the overflowed bits:
> * @addWithOverflow
> * @subWithOverflow
> * @mulWithOverflow
> * @shlWithOverflow

but in their definition says that it returns a `tuple`/`struct`.

Example;
`@addWithOverflow(a: anytype, b: anytype) struct { @TypeOf(a, b), u1 }`

Co-authored-by: zooster <r00ster91@proton.me>