waf: Add the ability to set FreeBSD options on the configure command line.

Add --freebsd-options to add specific FreeBSD compile time options to
the build. This is a developer tool.

freebsd/sys/kern/init_main.c

@@ -161,6 +161,11 @@ sysinit_add(struct sysinit **set, struct sysinit **set_end)
 	newsysinit_end = newset + count;
 }
 #else /* __rtems__ */
+#ifdef BOOTVERBOSE
+int	bootverbose = 1;
+SYSCTL_INT(_debug, OID_AUTO, bootverbose, CTLFLAG_RW, &bootverbose, 0,
+	"Control the output of verbose kernel messages");
+#endif
 RWSET_DECLARE(sysinit_set, struct sysinit);
 #endif /* __rtems__ */