[Bug c++/55203] No unused warning for variables of non-trivial types

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55203

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #6)
> std::lock_guard that is unused is useless.

Oops, I meant is *not* useless! Sorry.