[Bug libstdc++/119081] libstdc++.modules.json generated with incorrect relative path if configured with '--prefix=/' or '--prefix=' (empty)

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119081

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I am not even sure if prefix of / is valid use case. Shouldn't it be /usr ?