[Bug middle-end/115100] non-target specific const_scalar_int_operand predicate is not documented

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115100

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
>This has been true since wide-int branch was merged in back in 2014.

Actually older than that. I had missed understood the diff there. But still not
documented.