Contribs: fix vpx threading on Win32

(cherry picked from commit c51906de3a23ad6580c2c1373ef71d9c05f92993)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

contrib/src/vpx/libvpx-win32.patch

+--- libvpx/vp8/common/generic/systemdependent.c	2013-03-14 15:39:20.284261976 +0100
++++ libvpx.new/vp8/common/generic/systemdependent.c	2013-03-14 15:39:01.423974364 +0100
+@@ -87,7 +87,7 @@
+ #endif
+ 
+ 
+-#if HAVE_PTHREAD_H
++#if HAVE_PTHREAD_H && !defined(_WIN32)
+ #include <pthread.h>
+ static void once(void (*func)(void))
+ {

contrib/src/vpx/rules.mak

@@ -24,6 +24,9 @@ ifdef HAVE_MACOSX
 	$(APPLY) $(SRC)/vpx/libvpx-mac-mountain-lion.patch
 endif
 	$(PATCH_BASH_LOCATION)
+ifdef HAVE_WIN32
+	$(APPLY) $(SRC)/vpx/libvpx-win32.patch
+endif
 	$(MOVE)
 
 DEPS_vpx =