Make gyp work with Cygwin

tools/gyp/v8.gyp

 # Copyright 2012 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 734 matching lines @@
             ['OS=="mac"', {
               'sources': [
                 '../../src/platform-macos.cc',
                 '../../src/platform-posix.cc'
               ]},
             ],
             ['OS=="win"', {
               'variables': {
                 'gyp_generators': '<!(echo $GYP_GENERATORS)',
               },
-              'sources': [
-                '../../src/platform-win32.cc',
-                '../../src/win32-math.cc',
-                '../../src/win32-math.h',
-              ],
               'conditions': [
                 ['gyp_generators=="make"', {
+                  'variables': {
+                    'build_env': '<!(uname -o)',
+                  },
+                  'conditions': [
+                    ['build_env=="Cygwin"', {
+                      'sources': [
+                        '../../src/platform-cygwin.cc',
+                        '../../src/platform-posix.cc',
+                      ],
+                    }, {
+                      'sources': [
+                        '../../src/platform-win32.cc',
+                        '../../src/win32-math.h',
+                        '../../src/win32-math.cc',
+                      ],
+                    }],
+                  ],
                   'link_settings':  {
                     'libraries': [ '-lwinmm', '-lws2_32' ],
                   },
                 }, {
+                  'sources': [
+                    '../../src/platform-win32.cc',
+                    '../../src/win32-math.h',
+                    '../../src/win32-math.cc',
+                  ],
                   'msvs_disabled_warnings': [4351, 4355, 4800],
                   'link_settings':  {
                     'libraries': [ '-lwinmm.lib', '-lws2_32.lib' ],
                   },
                 }],
               ],
             }],
             ['component=="shared_library"', {
               'defines': [
                 'BUILDING_V8_SHARED',
@@ skipping 235 matching lines @@
             }],
           ],
           'dependencies': [
             'v8'
           ],
         },
       ],
     }],
   ],
 }