[Bug ada/81087] array index out of range in gnatlink, making test always false

[ebotcazou at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81087

--- Comment #9 from Eric Botcazou <ebotcazou at gcc dot gnu.org> ---
I agree that the change implemented in Is_Prefix is very likely unintentional
so reverting it is probably the best thing to do.  I'm going to apply the first
two patches to trunk and GCC 15 branches.