iwlwifi v6.11 started to use guard(). _T in the implementation needs
to be exposed to the driver which uses it in DEFINE_GUARD().
Given this is the first instance of attribute(cleanup) in the tree:
- gcc has support for it since at least 2003-06-04
(0bfa5f65bfb186f10d43304946fd7fcd69988732)
- llvm gained support on 2009-01-31
(d277d790e0f6f23043397ba919619b5c3e157ff3, llvm-svn 63462).
Sponsored by: The FreeBSD Foundation
Reviewed by: emaste
Differential Revision: https://reviews.freebsd.org/D46843
(cherry picked from commit fa81baa307da9a0055d7d08f6d141ea310f067ed)
