Prohibit string changes by "s"/"z" specifier of `mrb_get_args()`

- The `s` specifier is a string pointer obtained without performing `mrb_str_modify()`, so it cannot be changed.
- The `z` specifier cannot be changed because it is a string pointer obtained by `RSTRING_CSTR()` which returns `const char *`.

1 files changed, 2 insertions, 1 deletions

diff --git a/mrbgems/mruby-io/src/file.c b/mrbgems/mruby-io/src/file.c
index d3c4b3885..53ed4b69d 100644
--- a/mrbgems/mruby-io/src/file.c
+++ b/mrbgems/mruby-io/src/file.c
@@ -557,7 +557,8 @@ mrb_file_s_readlink(mrb_state *mrb, mrb_value klass) {
   mrb_raise(mrb, E_NOTIMP_ERROR, "readlink is not supported on this platform");
   return mrb_nil_value(); // unreachable
 #else
-  char *path, *buf, *tmp;
+  const char *path;
+  char *buf, *tmp;
   size_t bufsize = 100;
   ssize_t rc;
   mrb_value ret;