Fix warning for -Wmissing-prototypes

Source/astcenccli_internal.h

@@ -395,4 +395,16 @@ void launch_threads(
 	void (*func)(int, int, void*),
 	void *payload);
 
+/**
+ * @brief The main entry point.
+ *
+ * @param argc   The number of arguments.
+ * @param argv   The vector of arguments.
+ *
+ * @return 0 on success, non-zero otherwise.
+ */
+int astcenc_main(
+	int argc,
+	char **argv);
+
 #endif