mruby-exit/exit.c: add fallback definition of constants.
EXIT_SUCCESS
EXIT_FAILURE
#include <stdlib.h>
#include <mruby.h>
+#ifndef EXIT_SUCCESS
+# define EXIT_SUCCESS 0
+#endif
+
+#ifndef EXIT_FAILURE
+# define EXIT_FAILURE 1
+#endif
+
static mrb_value
f_exit(mrb_state *mrb, mrb_value self)
{
