The fallout of my making PTRACE conditional has made me realize that
#ifdefs in syscalls.master are never the right thing.  They just overly
complicate the code.  The only downside to no #ifdefs in syscall.master
is that *sysent.c always has a call to optional syscall.  This can
be resolved by including a include files which will #define the syscall
to sys_nosys.  Or the actual syscall could always return ENOSYS.

For the LKM case, declare the underlying syscall as a weak reference and
then test it for being non-zero at the start of the syscall.  We  
probably
should have a WEAK_SYSCALL(func) macro.

WEAK_SYSCALL(sys_ptrace);

int
foo_sys_ptrace(struct lwp *l, void *v, register_t *retval)
{
#if defined(PTRACE) || defined(_LKM)
#ifdef _LKM
	if (sys_ptrace == NULL)
		return ENOSYS;
#endif
	...
	...
#else
	return ENOSYS;
#endif /* PTRACE || _LKM */
}