[Bug libstdc++/96279] build failure: floating_from_chars.cc:310:22: error: '__builtin_isinf_sign' is not a member of 'std'

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96279

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Fixed by r11-2439 but I want to keep this open because the cross-config is
still wrong.