In sysv_sem.c, defer establishment of exithook so we can initialize the
module code from module_init() rather than waiting until after calling
exec_init().  Use a RUN_ONCE routine at entry to each sys_sem* syscall
to establish the exithook, and no longer KASSERT that the hook has
been set before removing it.  (A manually loaded module can be unloaded
before any syscalls have been invoked.)

Remove the conditional calls to the various xxx_init() routines from
init_main.c - we now rely on module_init() to handle initialization.

Let each sub-component's xxx_init() routine handle its own sysctl
sub-tree initialization;  this removes another set of #ifdef ugliness.

Tested both built-in and loadable versions and verified that atf
test kernel/t_sysv passes.


(pgoyette)