Update libvpx snapshot to v0.9.7-p1 (Cayuga).

source/libvpx/vpx_ports/x86.h

 /*
  *  Copyright (c) 2010 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 133 matching lines @@
 #endif
 #endif
 }
 
 
 #if defined(__GNUC__) && __GNUC__
 #define x86_pause_hint()\
     __asm__ __volatile__ ("pause \n\t")
 #else
 #if ARCH_X86_64
-/* No pause intrinsic for windows x64 */
-#define x86_pause_hint()
+#define x86_pause_hint()\
+    _mm_pause();
 #else
 #define x86_pause_hint()\
     __asm pause
 #endif
 #endif
 
 #if defined(__GNUC__) && __GNUC__
 static void
 x87_set_control_word(unsigned short mode)
 {
@@ skipping 32 matching lines @@
 {
     unsigned short mode = x87_get_control_word();
     x87_set_control_word((mode&~0x300) | 0x200);
     return mode;
 }
 
 
 extern void vpx_reset_mmx_state(void);
 #endif