make: Support '#' characters in defines.

test/defines/defines.gyp

 # Copyright (c) 2009 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': 'defines',
       'type': 'executable',
       'sources': [
         'defines.c',
       ],
       'defines': [
         'FOO',
         'VALUE=1',
         'PAREN_VALUE=(1+2+3)',
+        'HASH_VALUE="a#b"',
       ],
     },
   ],
   'conditions': [
     ['OS=="fakeos"', {
       'targets': [
         {
           'target_name': 'fakeosprogram',
           'type': 'executable',
           'sources': [
             'defines.c',
           ],
           'defines': [
             'FOO',
             'VALUE=1',
           ],
         },
       ],
     }],
   ],
 }