[Bug libstdc++/94933] std::fill_n delegates to __builtin_memset which is not constexpr

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94933

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Fixed on master, backport for gcc-10 will have to wait until after the 10.1
release.