Allow mutexes to take a lock ordering enum at construction.

This lets us specify whether and how mutexes of the same rank are allowed to be
acquired.  Currently, we only allow two polices (only a single mutex at a given
rank at a time, and mutexes acquired in ascending order), but we can plausibly
allow more (e.g. the "release uncontended mutexes before blocking").

src/ctl.c

@@ -1199,7 +1199,8 @@ label_return:
 
 bool
 ctl_boot(void) {
-	if (malloc_mutex_init(&ctl_mtx, "ctl", WITNESS_RANK_CTL)) {
+	if (malloc_mutex_init(&ctl_mtx, "ctl", WITNESS_RANK_CTL,
+	    malloc_mutex_rank_exclusive)) {
 		return true;
 	}