refactor assign variables

For readability.  Requested by ko1.

See: 356e203a3a (r35661401)

vm_eval.c

@@ -45,14 +45,11 @@ static VALUE vm_call0_body(rb_execution_context_t* ec, struct rb_calling_info *c
 MJIT_FUNC_EXPORTED VALUE
 rb_vm_call0(rb_execution_context_t *ec, VALUE recv, ID id, int argc, const VALUE *argv, const rb_callable_method_entry_t *me, int kw_splat)
 {
-    return vm_call0_body(
+    struct rb_calling_info calling = { Qundef, recv, argc, kw_splat, };
-        ec,
+    struct rb_call_info ci = { id, (kw_splat ? VM_CALL_KW_SPLAT : 0), argc, };
-        &(struct rb_calling_info) {
+    struct rb_call_cache cc = { 0, 0, me, me->def, vm_call_general, { 0, }, };
-            Qundef, recv, argc, kw_splat, },
+    struct rb_call_data cd = { cc, ci, };
-        &(struct rb_call_data) {
+    return vm_call0_body(ec, &calling, &cd, argv);
-            { 0, 0, me, me->def, vm_call_general, { 0, }, },
-            { id, (kw_splat ? VM_CALL_KW_SPLAT : 0), argc, }, },
-        argv);
 }
 
 static VALUE