Silence warnings from libnanomsg on Mac like we do on Linux.

gyp/nanomsg.gyp

 {
   'variables': {
     'skia_warnings_as_errors': 0,
   },
   'targets': [{
     # Draws pictures cross-process.
     'target_name': 'nanomsg_picture_demo',
     'type': 'executable',
     'dependencies': [
       'skia_lib.gyp:skia_lib',
@@ skipping 149 matching lines @@
           'NN_HAVE_SEMAPHORE',
           'NN_HAVE_SOCKETPAIR',
           'NN_USE_EPOLL',
           'NN_USE_EVENTFD',
           'NN_USE_IFADDRS',
           'STDC_HEADERS',
           '_GNU_SOURCE',
         ],
       }],
       ['skia_os == "mac"', {
+        'xcode_settings': {
+            'WARNING_CFLAGS': [ '-w' ],
+        },
         'defines=': [             # equals sign throws away most Skia defines (just noise)
           'HAVE_ARPA_INET_H',
           'HAVE_DLFCN_H',
           'HAVE_GETIFADDRS',
           'HAVE_INTTYPES_H',
           'HAVE_KQUEUE',
           'HAVE_MEMORY_H',
           'HAVE_NETDB_H',
           'HAVE_NETINET_IN_H',
           'HAVE_PIPE',
@@ skipping 18 matching lines @@
           'NN_USE_IFADDRS',
           'NN_USE_KQUEUE',
           'NN_USE_PIPE',
           'STDC_HEADERS',
           '_THREAD_SAFE',
         ],
       }],
     ]
   }]
 }