[Bug libstdc++/125624] C++23: support of std::float16_t for std::uniform_real_distribution

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125624

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
i.e. you're assuming that because some code happens to compile with GCC 15 that
it's supported. It's not. It's undefined.