sound_playsound() doesn't have to be visible externally,
so make it static.
diff --git a/PC/winsound.c b/PC/winsound.c
index bdc8b4c..c6f3a53 100644
--- a/PC/winsound.c
+++ b/PC/winsound.c
@@ -73,7 +73,7 @@
 "\n"
 "Beep(frequency, duration) - Make a beep through the PC speaker.");
 
-PyObject *
+static PyObject *
 sound_playsound(PyObject *s, PyObject *args)
 {
     const char *sound;