Already fixed upstream in https://github.com/sezero/mikmod/commit/4ceeed3f3929b9d9f7cfe891d44f43d202b64416.

Fixes -Wstrict-prototypes.
--- a/m4/libmikmod.m4
+++ b/m4/libmikmod.m4
@@ -79,7 +79,7 @@ char* my_strdup (char *str)
   return new_str;
 }
 
-int main()
+int main(void)
 {
   int major,minor,micro;
   int libmikmod_major_version,libmikmod_minor_version,libmikmod_micro_version;