[Bug c/59801] GCC does not warn on unused global variable

[su at cs dot ucdavis.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59801

--- Comment #6 from Zhendong Su <su at cs dot ucdavis.edu> ---
> *** This bug has been marked as a duplicate of bug 57258 ***

Andrew, I'm confused. The two are different, right?  57258 is about a possible
extra warning, and this one is about a missing warning.  What did I miss?
Thanks.