MDEV-17441 - InnoDB transition to C++11 atomics

ibuf_t::n_merges transition to Atomic_counter.

storage/innobase/ibuf/ibuf0ibuf.cc

@@ -4760,7 +4760,7 @@ ibuf_merge_or_delete_for_page(
 	btr_pcur_close(&pcur);
 	mem_heap_free(heap);
 
-	my_atomic_addlint(&ibuf->n_merges, 1);
+	ibuf->n_merges++;
 	ibuf_add_ops(ibuf->n_merged_ops, mops);
 	ibuf_add_ops(ibuf->n_discarded_ops, dops);
 
@@ -4897,7 +4897,7 @@ ibuf_print(
 		ibuf->size,
 		ibuf->free_list_len,
 		ibuf->seg_size,
-		ibuf->n_merges);
+		ulint{ibuf->n_merges});
 
 	fputs("merged operations:\n ", file);
 	ibuf_print_ops(ibuf->n_merged_ops, file);

storage/innobase/include/ibuf0ibuf.ic

@@ -78,7 +78,8 @@ struct ibuf_t{
 	ulint		height;		/*!< tree height */
 	dict_index_t*	index;		/*!< insert buffer index */
 
-	ulint		n_merges;	/*!< number of pages merged */
+	/** number of pages merged */
+	Atomic_counter<ulint> n_merges;
 	ulint		n_merged_ops[IBUF_OP_COUNT];
 					/*!< number of operations of each type
 					merged to index pages */