Bug 71972

When "options RESTARTABLE_PANICS" is enabled, gcc finds a warnings in
many source modules, like this:
..
/src/sys/fs/devfs/devfs_devs.c: In function `devfs_itor':
/src/sys/fs/devfs/devfs_devs.c:82: warning: control reaches end of non-void function
..
and then build fails because of -Werror.

The warnings like this one also found in:
/sys/kern/kern_intr.c
/sys/kern/subr_bus.c
/sys/kern/subr_witness.c

and possibly other places.

The warnings are appeared because RESTARTABLE_PANICS changes panic() prototype definition in sys/systm.h:324:

#ifdef RESTARTABLE_PANICS
void    panic(const char *, ...) __printflike(1, 2);
#else
void    panic(const char *, ...) __dead2 __printflike(1, 2);
#endif

Fix: 

I've tried to quickly fix a problem by inserting `for(;;);' aftel call to panic() in the files which are failed to compile, but after a 4 or 5 fixes decided that there must be 'a more right way' to fix this.
How-To-Repeat: Add an "options RESTARTABLE_PANICS" line into kernel configfile, then "make buildkernel" breaks.