ninja: Add target_rpath generator flag

test/linux/target-rpath/test.gyp

 # Copyright (c) 2013 Google Inc. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 {
   'targets': [
     {
       'target_name': 'shared',
       'type': 'shared_library',
       'sources': [ 'file.c' ],
     },
@@ skipping 27 matching lines @@
     {
       'target_name': 'static_executable',
       'type': 'executable',
       'sources': [ 'main.c' ],
       'dependencies': [
         'static',
       ]
     },
   ],
 }