When MSVC, "File.readlink fails with non-symlink" test was failed even if raising NotImplementedError

Fixed compile error of `mruby-io` gem on MinGW.

Fix memory leak found by leak sanitizer.

- `mode_t` by `int`
- `umask` by `_umask`
- `rmdir` by `_rmdir`
- `mkstemp` and `mkdtemp` by using `_mktemp`

git-subtree-dir: mrbgems/mruby-pack
git-subtree-mainline: 842e6945
git-subtree-split: 383a9c79

Also `bool` is a reserved word in C++.

git-subtree-dir: mrbgems/mruby-socket
git-subtree-mainline: d75266dd
git-subtree-split: ab541850

git-subtree-dir: mrbgems/mruby-io
git-subtree-mainline: 10ed730e
git-subtree-split: 3c8e1f94

The code was introduced to address #3175 but it's no longer needed.

Otherwise `super` may call a wrong method.

Mentioned in https://qiita.com/bamchoh/items/eabebbbb330cb0e0470a

Revise MRB_METHOD_PROC macro's argument

I revised MRB_METHOD_PROC macro's argument fn to m.

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

To avoid potential `malloc/free` mismatch.

And check required register number from `ci->proc` as well.
The fixes for #3859 and #3862 were incomplete.

Small performance improvement by reducing function invocations.

Should turn on `MRB_ENV_STACK_UNSHARED` flag only after env stack
reallocation.  `malloc()` may fail.