[Bug libstdc++/123167] to_chars(long double) produces rubbish with -mlong-double-64

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123167

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
>When the user changes the format, it's too late because the binary of libstdc++ has already set in stone the format of long double that to_chars supports.

That is NOT a supported, you need a multi-lib for libstdc++ for that option.

The documentation is clean on that too:
```
Warning: if you override the default value for your target ABI, this changes
the size of structures and arrays containing long double variables, as well as
modifying the function calling convention for functions taking long double.
Hence they are not binary-compatible with code compiled without that switch.

```