[Bug c/124830] c/c-decl.cc Fails to cross compile with C++20 host compiler

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124830

--- Comment #4 from Drea Pinski <pinskia at gcc dot gnu.org> ---
This was PR 117771 which was only fixed on the trunk for GCC 15.

You should be able to just backport
r15-5661-gf6e00226a4ca63e76e3e0b3a09a4ce6223980981 and that will fix the issue.