Fixed compiler warning

```
 ./src/joystick/SDL_joystick.c:105:12: warning: no previous extern declaration for non-static variable 'SDL_joystick_lock' [-Wmissing-variable-declarations]
SDL_mutex *SDL_joystick_lock = NULL; /* This needs to support recursive locks */
           ^
./src/joystick/SDL_joystick.c:105:1: note: declare 'static' if the variable is not intended to be used outside of this translation unit
SDL_mutex *SDL_joystick_lock = NULL; /* This needs to support recursive locks */
^
```
1 warning generated.

src/joystick/SDL_joystick.c

@@ -109,6 +109,10 @@ static SDL_JoystickDriver *SDL_joystick_drivers[] = {
         &SDL_DUMMY_JoystickDriver
 #endif
 };
+
+#ifndef SDL_THREAD_SAFETY_ANALYSIS
+static
+#endif
 SDL_mutex *SDL_joystick_lock = NULL; /* This needs to support recursive locks */
 static int SDL_joysticks_locked;
 static SDL_bool SDL_joysticks_initialized;

src/joystick/hidapi/SDL_hidapi_rumble.c

@@ -51,6 +51,9 @@ typedef struct SDL_HIDAPI_RumbleContext
     SDL_HIDAPI_RumbleRequest *requests_tail;
 } SDL_HIDAPI_RumbleContext;
 
+#ifndef SDL_THREAD_SAFETY_ANALYSIS
+static
+#endif
 SDL_mutex *SDL_HIDAPI_rumble_lock;
 static SDL_HIDAPI_RumbleContext rumble_context SDL_GUARDED_BY(SDL_HIDAPI_rumble_lock);