bpo-26219: per opcode cache for LOAD_GLOBAL (GH-12884)

This patch implements per opcode cache mechanism, and use it in
only LOAD_GLOBAL opcode.

Based on Yury's opcache3.patch in bpo-26219.

Python/pylifecycle.c

@@ -1242,6 +1242,9 @@ Py_FinalizeEx(void)
     /* Destroy all modules */
     PyImport_Cleanup();
 
+    /* Print debug stats if any */
+    _PyEval_Fini();
+
     /* Flush sys.stdout and sys.stderr (again, in case more was printed) */
     if (flush_std_files() < 0) {
         status = -1;