[NaCl SDK] Change the kernel_wrap OS #ifdefs in nacl_mounts.

native_client_sdk/src/libraries/nacl_mounts/kernel_wrap_win.cc

 /* Copyright (c) 2012 The Chromium Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
+// The entire file is wrapped in this #if. We do this so this .cc file can be
+// compiled, even on a non-Windows build.
+#if defined(WIN32)
+
 #include "nacl_mounts/kernel_wrap.h"
 #include <errno.h>
 #include <fcntl.h>
 #include <stdarg.h>
 #include <string.h>
 #include <sys/types.h>  // This must be included before <sys/stat.h>.
 #include <sys/stat.h>
 #include "nacl_mounts/kernel_intercept.h"
 
 namespace {
@@ skipping 193 matching lines @@
 
 int _unlink(const char* path) {
   return ki_unlink(path);
 }
 
 int _write(int fd, const void* buf, size_t nbyte) {
   return ki_write(fd, buf, nbyte);
 }
 
 EXTERN_C_END
+
+#endif   // defined(WIN32)