Revert "libavcodec/utils.c: simplify avcodec locking with atomics"

This reverts commit 590136e78d.

Atomics are not required for this variable, because it is protected
through the lock manager, and the use of atomics here is not compatible
with the c11 emulation wrappersi.

Fixes FATE on MSVC, among other setups which use the compat wrappers.

libavcodec/internal.h

@@ -241,6 +241,7 @@ int ff_init_buffer_info(AVCodecContext *s, AVFrame *frame);
 
 void ff_color_frame(AVFrame *frame, const int color[4]);
 
+extern volatile int ff_avcodec_locked;
 int ff_lock_avcodec(AVCodecContext *log_ctx, const AVCodec *codec);
 int ff_unlock_avcodec(const AVCodec *codec);
 

libavcodec/utils.c

@@ -115,7 +115,7 @@ static int (*lockmgr_cb)(void **mutex, enum AVLockOp op) = NULL;
 #endif
 
 
-static atomic_bool ff_avcodec_locked;
+volatile int ff_avcodec_locked;
 static atomic_int entangled_thread_counter = ATOMIC_VAR_INIT(0);
 static void *codec_mutex;
 static void *avformat_mutex;
@@ -1943,7 +1943,6 @@ int av_lockmgr_register(int (*cb)(void **mutex, enum AVLockOp op))
 
 int ff_lock_avcodec(AVCodecContext *log_ctx, const AVCodec *codec)
 {
-    _Bool exp = 0;
     if (codec->caps_internal & FF_CODEC_CAP_INIT_THREADSAFE || !codec->init)
         return 0;
 
@@ -1959,21 +1958,22 @@ int ff_lock_avcodec(AVCodecContext *log_ctx, const AVCodec *codec)
                atomic_load(&entangled_thread_counter));
         if (!lockmgr_cb)
             av_log(log_ctx, AV_LOG_ERROR, "No lock manager is set, please see av_lockmgr_register()\n");
-        atomic_store(&ff_avcodec_locked, 1);
+        ff_avcodec_locked = 1;
         ff_unlock_avcodec(codec);
         return AVERROR(EINVAL);
     }
-    av_assert0(atomic_compare_exchange_strong(&ff_avcodec_locked, &exp, 1));
+    av_assert0(!ff_avcodec_locked);
+    ff_avcodec_locked = 1;
     return 0;
 }
 
 int ff_unlock_avcodec(const AVCodec *codec)
 {
-    _Bool exp = 1;
     if (codec->caps_internal & FF_CODEC_CAP_INIT_THREADSAFE || !codec->init)
         return 0;
 
-    av_assert0(atomic_compare_exchange_strong(&ff_avcodec_locked, &exp, 0));
+    av_assert0(ff_avcodec_locked);
+    ff_avcodec_locked = 0;
     atomic_fetch_add(&entangled_thread_counter, -1);
     if (lockmgr_cb) {
         if ((*lockmgr_cb)(&codec_mutex, AV_LOCK_RELEASE))