Some OS uses `libedit` that does not provide `rl_free()`.
`libedit` is a `readline` compatible library with BSD license.
MODIFY
mrbgems/mruby-bin-mirb/tools/mirb/mirb.c
mrbgems/mruby-bin-mirb/tools/mirb/mirb.c
#include <readline/history.h>
#define MIRB_ADD_HISTORY(line) add_history(line)
#define MIRB_READLINE(ch) readline(ch)
+#if defined(__APPLE__) || defined(__NetBSD__) || defined(__OpenBSD__)
+/* libedit does not have rl_free() */
+#define MIRB_LINE_FREE(line) free(line)
+#else
#define MIRB_LINE_FREE(line) rl_free(line)
+#endif
#define MIRB_WRITE_HISTORY(path) write_history(path)
#define MIRB_READ_HISTORY(path) read_history(path)
#define MIRB_USING_HISTORY() using_history()

Some OS uses `libedit` that does not provide `rl_free()`.

`libedit` is a `readline` compatible library with BSD license.