optinfo-emit-json.cc: fix trivial memory leak

gcc/ChangeLog:
	* optinfo-emit-json.cc (class optrecord_json_writer): Convert
	field "m_scopes" from vec to auto_vec.

From-SVN: r262967

gcc/ChangeLog

+2018-07-25  David Malcolm  <dmalcolm@redhat.com>
+
+	* optinfo-emit-json.cc (class optrecord_json_writer): Convert
+	field "m_scopes" from vec to auto_vec.
+
 2018-07-25  Martin Liska  <mliska@suse.cz>
 
 	* config/powerpcspe/powerpcspe-protos.h (rs6000_loop_align): Fix

gcc/optinfo-emit-json.cc

@@ -75,7 +75,7 @@ private:
   json::array *m_root_tuple;
 
   /* The currently open scopes, for expressing nested optimization records.  */
-  vec<json::array *> m_scopes;
+  auto_vec<json::array *> m_scopes;
 };
 
 /* optrecord_json_writer's ctor.  Populate the top-level parts of the