various: remove ATOMIC_VAR_INIT

the fallback needed it due to the struct wrapper. but the fallback is
now removed so it's no longer needed.

as for standard atomics, it was never really needed either, was useless
and then made obsolete in C17 and removed in C23.

ref: https://gustedt.wordpress.com/2018/08/06/c17-obsoletes-atomic_var_init/
ref: https://en.cppreference.com/w/c/atomic/ATOMIC_VAR_INIT

common/msg.c

@@ -524,7 +524,7 @@ void mp_msg_init(struct mpv_global *global)
     struct mp_log_root *root = talloc_zero(NULL, struct mp_log_root);
     *root = (struct mp_log_root){
         .global = global,
-        .reload_counter = ATOMIC_VAR_INIT(1),
+        .reload_counter = 1,
     };
 
     pthread_mutex_init(&root->lock, NULL);

filters/f_async_queue.c

@@ -73,7 +73,7 @@ struct mp_async_queue *mp_async_queue_create(void)
     struct mp_async_queue *r = talloc_zero(NULL, struct mp_async_queue);
     r->q = talloc_zero(NULL, struct async_queue);
     *r->q = (struct async_queue){
-        .refcount = ATOMIC_VAR_INIT(1),
+        .refcount = 1,
     };
     pthread_mutex_init(&r->q->lock, NULL);
     talloc_set_destructor(r, on_free_queue);

misc/thread_tools.c

@@ -126,7 +126,7 @@ struct mp_cancel *mp_cancel_new(void *talloc_ctx)
     struct mp_cancel *c = talloc_ptrtype(talloc_ctx, c);
     talloc_set_destructor(c, cancel_destroy);
     *c = (struct mp_cancel){
-        .triggered = ATOMIC_VAR_INIT(false),
+        .triggered = false,
         .wakeup_pipe = {-1, -1},
     };
     pthread_mutex_init(&c->lock, NULL);

osdep/windows_utils.c

@@ -164,7 +164,7 @@ char *mp_HRESULT_to_str_buf(char *buf, size_t buf_size, HRESULT hr)
 bool mp_w32_create_anon_pipe(HANDLE *server, HANDLE *client,
                              struct w32_create_anon_pipe_opts *opts)
 {
-    static atomic_ulong counter = ATOMIC_VAR_INIT(0);
+    static atomic_ulong counter = 0;
 
     // Generate pipe name
     unsigned long id = atomic_fetch_add(&counter, 1);

sub/osd.c

@@ -126,7 +126,7 @@ struct osd_state *osd_create(struct mpv_global *global)
         .opts_cache = m_config_cache_alloc(osd, global, &mp_osd_render_sub_opts),
         .global = global,
         .log = mp_log_new(osd, global->log, "osd"),
-        .force_video_pts = ATOMIC_VAR_INIT(MP_NOPTS_VALUE),
+        .force_video_pts = MP_NOPTS_VALUE,
         .stats = stats_ctx_create(osd, global, "osd"),
     };
     pthread_mutex_init(&osd->lock, NULL);

video/out/dr_helper.c

@@ -44,7 +44,7 @@ struct dr_helper *dr_helper_create(struct mp_dispatch_queue *dispatch,
     talloc_set_destructor(dr, dr_helper_destroy);
     *dr = (struct dr_helper){
         .dispatch = dispatch,
-        .dr_in_flight = ATOMIC_VAR_INIT(0),
+        .dr_in_flight = 0,
         .get_image = get_image,
         .get_image_ctx = get_image_ctx,
     };