[Bug libstdc++/60401] stdlib.h does not provide abs(long) overload

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60401

--- Comment #16 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #15)
> After discussing this on IRC I'll make a change to support this use case,
> without needing to rebuild libstdc++ when glibc is updated.

I've created https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69413 for that.