Update NSPR to 4.12 and NSS to 3.23 on iOS

nspr/pr/include/md/_linux.h

 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 /*
  * This file is used by not only Linux but also other glibc systems
  * such as GNU/Hurd and GNU/k*BSD.
  */
 
@@ skipping 653 matching lines @@
 extern PRStatus _MD_WAIT(PRThread *, PRIntervalTime timeout);
 extern PRStatus _MD_WAKEUP_WAITER(PRThread *);
 extern void _MD_YIELD(void);
 
 #endif /* ! _PR_PTHREADS */
 
 extern void _MD_EarlyInit(void);
 
 #define _MD_EARLY_INIT                  _MD_EarlyInit
 #define _MD_FINAL_INIT                  _PR_UnixInit
-#define HAVE_CLOCK_MONOTONIC
+#define _PR_HAVE_CLOCK_MONOTONIC
 
 /*
  * We wrapped the select() call.  _MD_SELECT refers to the built-in,
  * unwrapped version.
  */
 #define _MD_SELECT __select
 
 #ifdef _PR_POLL_AVAILABLE
 #include <sys/poll.h>
 extern int __syscall_poll(struct pollfd *ufds, unsigned long int nfds,
         int timeout);
 #define _MD_POLL __syscall_poll
 #endif
 
 /* For writev() */
 #include <sys/uio.h>
 
 extern void _MD_linux_map_sendfile_error(int err);
 
 #endif /* nspr_linux_defs_h___ */