(https://github.com/ruby/fiddle/pull/109)

These structs don't need to be freed as part of finalization, so lets
free them immediately.

https://github.com/ruby/fiddle/commit/8a10ec1152

GitHub: fix https://github.com/ruby/fiddle/pull/107

Reported by nicholas a. evans. Thanks!!!

https://github.com/ruby/fiddle/commit/49ea1490df

Fiddle is a gem and has the external upstream which supports older
versions of Ruby.

https://bugs.ruby-lang.org/issues/18571

Co-authored-by: Nobuyoshi Nakada <nobu@ruby-lang.org>
Co-authored-by: Sutou Kouhei <kou@clear-code.com>

GitHub: GH-102

https://github.com/ruby/fiddle/commit/2530496602

GitHub: GH-102

https://github.com/ruby/fiddle/commit/81a8a56239

GitHub: fix GH-102

It's for freeing a closure explicitly.

We can't use Fiddle::Closure before we fork the process. If we do it,
the process may be crashed with SELinux.

See https://github.com/ruby/fiddle/issues/102#issuecomment-1241763091
for details.

Reported by Vít Ondruch. Thanks!!!

https://github.com/ruby/fiddle/commit/a0ccc6bb1b

I would like to check if a symbol is defined before trying to access it.
Some symbols aren't available on all platforms, so instead of raising an
exception, I want to check if it's defined first.

Today we have to do:

```ruby
begin
  addr = Fiddle::Handle.sym("something")
  # do something
rescue Fiddle::DLError
end
```

I want to write this:

```ruby
if Fiddle::Handle.sym_defined?("something")
  addr = Fiddle::Handle.sym("something")
  # do something
end
```

https://github.com/ruby/fiddle/commit/9d3371de13

Co-authored-by: Sutou Kouhei <kou@clear-code.com>