[ffvpx] Update ffvp9/ffvp8 to 3.4.2-release

Structure of code was slightly modified so that it should be no longer necessary to re-generate the config_*.h files, greatly simplifying the resync process in the future.

media/ffvpx/libavutil/cpu.h

@@ -21,6 +21,8 @@
 #ifndef AVUTIL_CPU_H
 #define AVUTIL_CPU_H
 
+#include <stddef.h>
+
 #include "attributes.h"
 
 #define AV_CPU_FLAG_FORCE    0x80000000 /* force usage of selected flags (OR) */
@@ -39,6 +41,7 @@
 #define AV_CPU_FLAG_SSE3SLOW 0x20000000 ///< SSE3 supported, but usually not faster
                                         ///< than regular MMX/SSE (e.g. Core1)
 #define AV_CPU_FLAG_SSSE3        0x0080 ///< Conroe SSSE3 functions
+#define AV_CPU_FLAG_SSSE3SLOW 0x4000000 ///< SSSE3 supported, but usually not faster
 #define AV_CPU_FLAG_ATOM     0x10000000 ///< Atom processor, some SSSE3 instructions are slower
 #define AV_CPU_FLAG_SSE4         0x0100 ///< Penryn SSE4.1 functions
 #define AV_CPU_FLAG_SSE42        0x0200 ///< Nehalem SSE4.2 functions
@@ -85,8 +88,6 @@ void av_force_cpu_flags(int flags);
  * Set a mask on flags returned by av_get_cpu_flags().
  * This function is mainly useful for testing.
  * Please use av_force_cpu_flags() and av_get_cpu_flags() instead which are more flexible
- *
- * @warning this function is not thread safe.
  */
 attribute_deprecated void av_set_cpu_flags_mask(int mask);
 
@@ -114,4 +115,15 @@ int av_parse_cpu_caps(unsigned *flags, const char *s);
  */
 int av_cpu_count(void);
 
+/**
+ * Get the maximum data alignment that may be required by FFmpeg.
+ *
+ * Note that this is affected by the build configuration and the CPU flags mask,
+ * so e.g. if the CPU supports AVX, but libavutil has been built with
+ * --disable-avx or the AV_CPU_FLAG_AVX flag has been disabled through
+ *  av_set_cpu_flags_mask(), then this function will behave as if AVX is not
+ *  present.
+ */
+size_t av_cpu_max_align(void);
+
 #endif /* AVUTIL_CPU_H */