Should enable C++ exceptions for all targets on Windows.

It's a requirement for using standard library of VS.

atom.gyp

@@ -252,14 +252,6 @@
         '.',
         'vendor',
       ],
-      'msvs_settings': {
-        'VCCLCompilerTool': {
-          # Programs that use the Standard C++ library must be compiled with C++
-          # exception handling enabled.
-          # http://support.microsoft.com/kb/154419
-          'ExceptionHandling': 1,
-        },
-      },
     },
     {
       'target_name': 'generated_sources',

common.gypi

@@ -77,5 +77,18 @@
         },
       },
     }],  # clang==1
+    # Windows specific settings.
+    ['OS=="win"', {
+      'target_defaults': {
+        'msvs_settings': {
+          'VCCLCompilerTool': {
+            # Programs that use the Standard C++ library must be compiled with C++
+            # exception handling enabled.
+            # http://support.microsoft.com/kb/154419
+            'ExceptionHandling': 1,
+          },
+        },
+      },
+    }],  # OS=="win"
   ],
 }