Prepare for removal of source_filter.gypi:

runtime/bin/socket_macos.cc

Index: runtime/bin/socket_macos.cc
===================================================================
--- runtime/bin/socket_macos.cc	(revision 18775)
+++ runtime/bin/socket_macos.cc	(working copy)
@@ -2,13 +2,16 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-#include <errno.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-#include <sys/stat.h>
-#include <unistd.h>
+#include "platform/globals.h"
+#if defined(TARGET_OS_MACOS)
 
+#include <errno.h>  // NOLINT
+#include <stdio.h>  // NOLINT
+#include <stdlib.h>  // NOLINT
+#include <string.h>  // NOLINT
+#include <sys/stat.h>  // NOLINT
+#include <unistd.h>  // NOLINT
+
 #include "bin/fdutils.h"
 #include "bin/file.h"
 #include "bin/log.h"
@@ -262,3 +265,5 @@
     Log::PrintErr("%s\n", error_message);
   }
 }
+
+#endif  // defined(TARGET_OS_MACOS)