Automatically exclude platform-specific files for all targets

This way embedding applications don't have to do this themselves, as long as
they follow our naming conventions.

brightray/brightray.gyp

@@ -72,11 +72,6 @@
               '$(SDKROOT)/System/Library/Frameworks/AppKit.framework',
             ],
           },
-        }, {
-          'sources/': [
-            ['exclude', '/mac/'],
-            ['exclude', '_mac\.(mm|h)$'],
-          ],
         }],
         ['OS=="win"', {
           'link_settings': {
@@ -86,11 +81,6 @@
               '<(libchromiumcontent_library_dir)/sandbox_static.lib',
             ],
           },
-        }, {
-          'sources/': [
-            ['exclude', '/win/'],
-            ['exclude', '_win\.(cc|h)$'],
-          ],
         }],
       ],
     },

brightray/brightray.gypi

@@ -153,6 +153,20 @@
         },
       },
     },
+    'conditions': [
+      ['OS!="mac"', {
+        'sources/': [
+          ['exclude', '/mac/'],
+          ['exclude', '_mac\.(mm|h)$'],
+        ],
+      }],
+      ['OS!="win"', {
+        'sources/': [
+          ['exclude', '/win/'],
+          ['exclude', '_win\.(cc|h)$'],
+        ],
+      }],
+    ],
   },
   'conditions': [
     ['OS=="win"', {