[PATCH] libstdc++: Add _Float128 to_chars/from_chars support for x86, ia64 and ppc64le with glibc

[Joseph Myers]

On Mon, 7 Nov 2022, Jonathan Wakely wrote:

> This seems to "fix" it (not sure if it's right though):
> 
> #ifndef _GLIBCXX_HAVE_FLOAT128_MATH
> extern "C" _Float128 __strtof128(const char*, char**)
>  __attribute__((__weak__));
> #endif
> extern "C" _Float128 __strtof128(const char*, char**)
>  __asm ("strtof128");

Probably putting the __asm before the __attribute__ would also work 
without needing a separate declaration (but might be less convenient for 
the #if conditionals).

-- 
Joseph S. Myers
joseph@codesourcery.com