libvpx: Pull from upstream

source/libvpx/vpx_ports/vpx_once.h

 /*
  *  Copyright (c) 2011 The WebM project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 55 matching lines @@
      */
     if(!InterlockedDecrement(&waiters))
     {
         DeleteCriticalSection(lock);
         free(lock);
         lock = NULL;
     }
 }
 
 
+#elif CONFIG_MULTITHREAD && defined(__OS2__)
+#define INCL_DOS
+#include <os2.h>
+static void once(void (*func)(void))
+{
+    static int done;
+
+    /* If the initialization is complete, return early. */
+    if(done)
+        return;
+
+    /* Causes all other threads in the process to block themselves
+     * and give up their time slice.
+     */
+    DosEnterCritSec();
+
+    if (!done)
+    {
+        func();
+        done = 1;
+    }
+
+    /* Restores normal thread dispatching for the current process. */
+    DosExitCritSec();
+}
+
+
 #elif CONFIG_MULTITHREAD && HAVE_PTHREAD_H
 #include <pthread.h>
 static void once(void (*func)(void))
 {
     static pthread_once_t lock = PTHREAD_ONCE_INIT;
     pthread_once(&lock, func);
 }
 
 
 #else
 /* No-op version that performs no synchronization. vp8_rtcd() is idempotent,
  * so as long as your platform provides atomic loads/stores of pointers
  * no synchronization is strictly necessary.
  */
 
 static void once(void (*func)(void))
 {
     static int done;
 
     if(!done)
     {
         func();
         done = 1;
     }
 }
 #endif
 
 #endif  // VPX_PORTS_VPX_ONCE_H_