[Bug libstdc++/80196] fenv_t not declared

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80196

--- Comment #16 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Eddy L O Jansson from comment #15)
> For reasons that I'll skip, between the successful build of 12.0.1 and now I
> had added:
> 
> export
> CPLUS_INCLUDE_PATH=/opt/local/include/c++/12.0.1:/opt/local/include/c++/12.0.
> 1/x86_64-linux-gnu/
> 
> to my .bashrc

Don't do that. This causes GCC 12.1 to find the headers for GCC 12.0.1 instead
of the libc headers. That breaks the build, but is user error.