drm-shim: use atomics for inited

This is more thread safe.

This is still broken, because another thread could use the global
variables after inited is set but before the shim is fully initialized,
but I guess it's better than before.

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37055>

src/drm-shim/drm_shim.c

@@ -204,18 +204,14 @@ destroy_shim(void)
 static void
 init_shim(void)
 {
-   static bool inited = false;
+   static uint32_t inited = 0;
+
    drm_shim_debug = debug_get_bool_option("DRM_SHIM_DEBUG", false);
 
    /* We can't lock this, because we recurse during initialization. */
-   if (inited)
+   if (p_atomic_cmpxchg(&inited, 0, 1))
       return;
 
-   /* This comes first (and we're locked), to make sure we don't recurse
-    * during initialization.
-    */
-   inited = true;
-
    opendir_set = _mesa_set_create(NULL,
                                   _mesa_hash_string,
                                   _mesa_key_string_equal);