linux: Link with breakpad_client.

atom.gyp

@@ -411,6 +411,9 @@
               '-rdynamic',
             ],
           },
+          'dependencies': [
+            'vendor/breakpad/breakpad.gyp:breakpad_client',
+          ],
         }],  # OS=="linux"
       ],
     },  # target <(product_name)_lib

common.gypi

@@ -31,6 +31,8 @@
     'node_use_perfctr': 'false',
     'node_use_systemtap': 'false',
     'v8_postmortem_support': 'false',
+    # Required by Linux (empty for now, should support it in future).
+    'sysroot': '',
   },
   # Settings to compile node under Windows.
   'target_defaults': {