[committed] libstdc++: Define std::numeric_limits<_FloatNN> before C++23

[Jakub Jelinek]

On Wed, Oct 04, 2023 at 09:47:34AM -0700, Pranav Kant wrote:
> Thanks for bringing this to my attention. I am working on a fix. Will keep
> this thread posted.
> 
> Clang *does* define this macro only when float128 type is available. But
> the problem seems to be that clang doesn't define _Float128 alias type
> which is what's being used here. It only defines __float128 type. Should be
> easy to fix.

_Float128 (and other _FloatNN types) are standard C23 and C++23 types,
they certainly can't be simple aliases to __float128 or other similar types.
In C++ they mangle differently, have significantly different behavior in
lots of different language details.
So, you need to implement the https://wg21.link/P1467R9 paper, rather than
doing quick hacks.

	Jakub