Use (void) for function prototypes with no parameters

This is required when compiling these headers as C code. These were
omitted becuase before the addition of examples these headers were
only compiled locally as C++ files where adding the void keyword is
not needed.

include/SFML/Audio/SoundRecorder.h

@@ -157,7 +157,7 @@ CSFML_AUDIO_API const char** sfSoundRecorder_getAvailableDevices(size_t* count);
 /// \return The name of the default audio capture device (null terminated)
 ///
 ////////////////////////////////////////////////////////////
-CSFML_AUDIO_API const char* sfSoundRecorder_getDefaultDevice();
+CSFML_AUDIO_API const char* sfSoundRecorder_getDefaultDevice(void);
 
 ////////////////////////////////////////////////////////////
 /// \brief Set the audio capture device