Enable RGBGFX's CLI "at-files" for all programs (#1848)

include/cli.hpp

@@ -0,0 +1,20 @@
+// SPDX-License-Identifier: MIT
+
+#ifndef RGBDS_CLI_HPP
+#define RGBDS_CLI_HPP
+
+#include <stdarg.h>
+#include <string>
+
+#include "extern/getopt.hpp" // option
+
+void cli_ParseArgs(
+    int argc,
+    char *argv[],
+    char const *shortOpts,
+    option const *longOpts,
+    void (*parseArg)(int, char *),
+    void (*fatal)(char const *, ...)
+);
+
+#endif // RGBDS_CLI_HPP