[Bug libstdc++/70560] Review configure checks for _GLIBCXX_ATOMIC_BUILTINS and atomicity_dir

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70560

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to James Hilliard from comment #2)
> We've been hitting a bug in buildroot with an application(apcupsd) that
> links against libsupc++.a directly.

Maybe I missed it, but I don't see the linker command in the build log. Could
you show the command that's failing? Could you check if the symbol
_ZN9__gnu_cxx18__exchange_and_addEPVii is actually defined in libsupc++.a or if
something else like _ZN9__gnu_cxx18__exchange_and_addEPVll is defined instead?