[Bug libstdc++/104870] [12 Regression] fast_float doesn't work for 16-bit size_t, but is used anyway by floating_from_chars.cc

[dv at vollmann dot ch via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104870

--- Comment #7 from dv at vollmann dot ch ---
Tested for AVR, works :-)
Thanks,
  Detlef