[Bug libstdc++/126452] Typo in check for --gc-sections support in acinclude.m4

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126452

--- Comment #13 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Andreas Schwab from comment #11)
> Or just leave it out.

Yeah "arning" would have worked, but would have looked like another typo and
somebody probably would have corrected it :-)