hints: Added SDL_HINT_LOG_BACKENDS.

Fixes #13354.

include/SDL3/SDL_hints.h

@@ -4381,6 +4381,27 @@ extern "C" {
  */
 #define SDL_HINT_PEN_TOUCH_EVENTS "SDL_PEN_TOUCH_EVENTS"
 
+/**
+ * A variable controlling whether SDL backend information is logged.
+ *
+ * The variable can be set to the following values:
+ *
+ * - "0": Subsystem information will not be logged. (default)
+ * - "1": Subsystem information will be logged.
+ *
+ * This is generally meant to be used as an environment variable to let
+ * end-users report what subsystems were chosen on their system, to aid
+ * in debugging. Logged information is sent through SDL_Log(), which
+ * means by default they appear on stdout on most platforms or maybe
+ * OutputDebugString() on Windows, and can be funneled by the app with
+ * SDL_SetLogOutputFunction(), etc.
+ *
+ * This hint can be set anytime, but the specific logs are generated
+ * during subsystem init.
+ *
+ * \since This hint is available since SDL 3.4.0.
+ */
+#define SDL_HINT_LOG_BACKENDS "SDL_LOG_BACKENDS"
 
 /**
  * An enumeration of hint priorities.