Fix -Wsign-compare warnings under GCC 6.2

Author: rtsisyk

small/region.c

@@ -69,8 +69,8 @@ region_free(struct region *region)
 void
 region_truncate(struct region *region, size_t used)
 {
-	ssize_t cut_size = region_used(region) - used;
-	assert(cut_size >= 0);
+	assert(region_used(region) >= used);
+	size_t cut_size = region_used(region) - used;
 
 	while (! rlist_empty(&region->slabs.slabs)) {
 		struct rslab *slab = rlist_first_entry(&region->slabs.slabs,

small/slab_cache.c

@@ -158,7 +158,7 @@ slab_cache_create(struct slab_cache *cache, struct slab_arena *arena)
 	 * of the slab size in the slab arena.
 	 */
 	long min_order0_size = sysconf(_SC_PAGESIZE);
-	assert(arena->slab_size >= min_order0_size);
+	assert((long)arena->slab_size >= min_order0_size);
 	cache->order_max = small_lb(arena->slab_size / min_order0_size);
 	if (cache->order_max > ORDER_MAX - 1)
 		cache->order_max = ORDER_MAX - 1;