use more distinctive pattern to mark where dart source goes

runtime/bin/builtin_in.cc

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include <assert.h>
 #include <stdlib.h>
 #include <string.h>
 
 #include "include/dart_api.h"
 
 #include "bin/builtin.h"
 #include "bin/dartutils.h"
 
 // The string on the next line will be filled in with the contents of the
 // builtin.dart file.
 // This string forms the content of builtin functionality which is injected
 // into standalone dart to provide some test/debug functionality.
 static const char Builtin_source_[] = {
-  %s
+  {{DART_SOURCE}}
 };
 
 
 // List all native functions implemented in standalone dart that is used
 // to inject additional functionality e.g: Logger, file I/O, socket I/O etc.
 #define BUILTIN_NATIVE_LIST(V)                                                 \
   V(Logger_PrintString, 1)                                                     \
   V(Directory_List, 7)                                                         \
   V(Directory_Exists, 2)                                                       \
   V(Directory_Create, 2)                                                       \
@@ skipping 119 matching lines @@
 
 
 void Builtin_SetNativeResolver() {
   Dart_Handle url = Dart_NewString(DartUtils::kBuiltinLibURL);
   Dart_Result result = Dart_LookupLibrary(url);
   assert(Dart_IsValidResult(result));
   Dart_Handle builtin_lib = Dart_GetResult(result);
   result = Dart_SetNativeResolver(builtin_lib, native_lookup);
   assert(Dart_IsValidResult(result));
 }