p->p_intr_nesting_level is MI now and initialized to 0 in kern_fork.c,

so it should be save to KASSERT() on it even on an arch that may not
use it.

sys/kern/kern_malloc.c

@@ -146,7 +146,7 @@ malloc(size, type, flags)
 #endif
 	register struct malloc_type *ksp = type;
 
-#if defined(INVARIANTS) && defined(__i386__)
+#if defined(INVARIANTS)
 	if (flags == M_WAITOK)
 		KASSERT(curproc->p_intr_nesting_level == 0,
 		   ("malloc(M_WAITOK) in interrupt context"));