mark some conditions as unlikely

* assertion failure
* malloc_init failure
* malloc not already initialized (in malloc_init)
* running in valgrind
* thread cache disabled at runtime

Clang and GCC already consider a comparison with NULL or -1 to be cold,
so many branches (out-of-memory) are already correctly considered as
cold and marking them is not important.

include/jemalloc/internal/tcache.h

@@ -218,7 +218,7 @@ tcache_get(bool create)
 		return (NULL);
 
 	tcache = *tcache_tsd_get();
-	if ((uintptr_t)tcache <= (uintptr_t)TCACHE_STATE_MAX) {
+	if (unlikely((uintptr_t)tcache <= (uintptr_t)TCACHE_STATE_MAX)) {
 		if (tcache == TCACHE_STATE_DISABLED)
 			return (NULL);
 		tcache = tcache_get_hard(tcache, create);