[Bug libstdc++/71090] #include cannot locate math.h

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71090

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
If you mess with the order of system header directories then you mess up how
headers are found. So don't do that.