[Bug c/124830] [13/14 only] c/c-decl.cc Fails to cross compile with C++20 host compiler

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

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

--- Comment #9 from Richard Biener <rguenth at gcc dot gnu.org> ---
I'll just bring branches in-line with what we effectively have on 15/trunk, not
doing any further changes there.