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

["unlvsur at live dot com" <gcc-bugzilla@gcc.gnu.org>]

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

--- Comment #28 from cqwrteur <unlvsur at live dot com> ---
(In reply to Ofer Shinaar from comment #27)
> (In reply to cqwrteur from comment #23)
> > (In reply to Jonathan Wakely from comment #22)
> > > *** Bug 101060 has been marked as a duplicate of this bug. ***
> > 
> > I can confirm Yujie Yang's patch works. Just add -nostdinc++ to configure
> > and configure.ac in gcc root repository (not in gcc subdirectory nor
> > libstdc++-v3 subdirectory)
> > 
> > Yes. So it is very easy to fix.
> 
> and what if I do want to use libstdc++ ? the first soultion allows me that

no. it does not affect how libstdc++ builds. It is a bug in the build process
that the GCC will prefer finding headers in the C++ cross compiler. It should
not use C++ standard library headers in your cross compiler.

Add -nostdinc++ is adding a toggle at the build process that fixes all sorts of
issues that relate to the build of libstdc++.

It won't affect you for using it after the build.

There are some other problems of Canadian compilation here, like copying wrong
DLLs when you build with multilibs. Those are separate issues.