Update SDL to the latest source code (2.0.9 + e1e13e154128)

libs/SDL2/src/audio/SDL_audiodev_c.h

@@ -18,6 +18,10 @@
      misrepresented as being the original software.
   3. This notice may not be removed or altered from any source distribution.
 */
+
+#ifndef SDL_audiodev_c_h_
+#define SDL_audiodev_c_h_
+
 #include "SDL.h"
 #include "../SDL_internal.h"
 #include "SDL_sysaudio.h"
@@ -35,4 +39,6 @@
 
 extern void SDL_EnumUnixAudioDevices(const int classic, int (*test)(int));
 
+#endif /* SDL_audiodev_c_h_ */
+
 /* vi: set ts=4 sw=4 expandtab: */