Index: sys/kern/kern_resource.c
===================================================================
--- sys/kern/kern_resource.c
+++ sys/kern/kern_resource.c
@@ -80,8 +80,6 @@
 static struct uidinfo *uilookup(uid_t uid);
 static void	ruxagg_locked(struct rusage_ext *rux, struct thread *td);
 
-static __inline int	lim_shared(struct plimit *limp);
-
 /*
  * Resource controls and accounting.
  */
@@ -1109,6 +1107,8 @@
 	return (limp);
 }
 
+/* Fix -Wunused warning with clang by only exposing lim_shared with INVARIANTS. */
+#ifdef INVARIANTS
 static __inline int
 lim_shared(struct plimit *limp)
 {
@@ -1115,6 +1115,7 @@
 
 	return (limp->pl_refcnt > 1);
 }
+#endif
 
 void
 lim_fork(struct proc *p1, struct proc *p2)
@@ -1146,7 +1147,9 @@
 lim_copy(struct plimit *dst, struct plimit *src)
 {
 
+#ifdef INVARIANTS
 	KASSERT(!lim_shared(dst), ("lim_copy to shared limit"));
+#endif
 	bcopy(src->pl_rlimit, dst->pl_rlimit, sizeof(src->pl_rlimit));
 }