[Bug libstdc++/100017] [11/12 regression] error: 'fenv_t' has not been declared in '::' -- canadian compilation fails

[unlvsur at live dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100017

--- Comment #49 from cqwrteur <unlvsur at live dot com> ---
https://gcc.gnu.org/pipermail/gcc-patches/2021-December/587254.html

I just send an email to add a patch for this. Jonathan Wakely, can you review
the patch here?