ifdef RACCT ui_racct_foreach and struct uidinfo's ui_racct

Change racct_ create and destroy to macros evaluating to nothing without RACCT
so that their callers passing ui_racct don't have to be ifdefed.
Do not include buf.h.
Merge remote-tracking branch 'freebsd/master' into hardened/current/master
Merge remote-tracking branch 'origin/hardened/current/master' into hardened/current/segvguard