lavc: provide deprecated avcodec_thread_init until next major version

It was deprecated only recently.

libavcodec/avcodec.h

@@ -3577,6 +3577,14 @@ void avcodec_align_dimensions2(AVCodecContext *s, int *width, int *height,
 
 enum PixelFormat avcodec_default_get_format(struct AVCodecContext *s, const enum PixelFormat * fmt);
 
+#if FF_API_THREAD_INIT
+/**
+ * @deprecated Set s->thread_count before calling avcodec_open() instead of calling this.
+ */
+attribute_deprecated
+int avcodec_thread_init(AVCodecContext *s, int thread_count);
+#endif
+
 int avcodec_default_execute(AVCodecContext *c, int (*func)(AVCodecContext *c2, void *arg2),void *arg, int *ret, int count, int size);
 int avcodec_default_execute2(AVCodecContext *c, int (*func)(AVCodecContext *c2, void *arg2, int, int),void *arg, int *ret, int count);
 //FIXME func typedef

libavcodec/utils.c

@@ -1220,3 +1220,11 @@ void ff_thread_await_progress(AVFrame *f, int progress, int field)
 }
 
 #endif
+
+#if FF_API_THREAD_INIT
+int avcodec_thread_init(AVCodecContext *s, int thread_count)
+{
+    s->thread_count = thread_count;
+    return ff_thread_init(s);
+}
+#endif

libavcodec/version.h

@@ -65,5 +65,8 @@
 #ifndef FF_API_OPT_H
 #define FF_API_OPT_H            (LIBAVCODEC_VERSION_MAJOR < 54)
 #endif
+#ifndef FF_API_THREAD_INIT
+#define FF_API_THREAD_INIT      (LIBAVCODEC_VERSION_MAJOR < 54)
+#endif
 
 #endif /* AVCODEC_VERSION_H */