[Bug ada/125695] Big_Exp special case for (+/-)2 ** K is broken for -2 and even K

[ebotcazou at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125695

--- Comment #13 from Eric Botcazou <ebotcazou at gcc dot gnu.org> ---
Yes, I'll make a pass over Big_Div, Big_Mod and Big_Rem.