Ensure mjsunit tests use dashes not underscores in flags directives.

test/mjsunit/declare-locally.js

 // Copyright 2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 15 matching lines @@
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 // Make sure that we're not overwriting global
 // properties defined in the prototype chain too
 // early when shadowing them with var/const
 // declarations.
 
 // This exercises the code in runtime.cc in
 // DeclareGlobal...Locally().
 
-// Flags: --es52_globals
+// Flags: --es52-globals
 
 this.__proto__.foo = 42;
 this.__proto__.bar = 87;
 
 eval("assertEquals(undefined, foo); var foo = 87;");
 assertEquals(87, foo);
 
 eval("assertEquals(undefined, bar); const bar = 42;");
 assertEquals(42, bar);