On OpenBSD, USE_FFI_CLOSURE_ALLOC was always set to 0 previously. In
633a1f15d8228236094ddee12e4e169d655ec49e, the code was modified in a
way that it ended up being set to 1 on OpenBSD.  However, that results
in SIGABRT when running make test-all, inside ffi_closure_free.
Setting USE_FFI_CLOSURE_ALLOC back to 0 fixes the issue.

This reverts commit 87f6154bb4c67ca77ee353bb1fe25a922036c0e5.

It turned out that the change fails to build on macOS

https://rubyci.org/logs/rubyci.s3.amazonaws.com/osx1014/ruby-master/log/20200304T074503Z.fail.html.gz
```
+ make 'TESTS=--hide-skip -v fiddle' RUBYOPT=-w test-all
dyld: lazy symbol binding failed: Symbol not found: _ffi_closure_alloc
  Referenced from: /Users/hsbt/Documents/cb/tmp/build/20200304T074503Z/ruby/.ext/x86_64-darwin18/fiddle.bundle
  Expected in: flat namespace

dyld: Symbol not found: _ffi_closure_alloc
  Referenced from: /Users/hsbt/Documents/cb/tmp/build/20200304T074503Z/ruby/.ext/x86_64-darwin18/fiddle.bundle
  Expected in: flat namespace

make: *** [yes-test-all] Abort trap: 6
```

This reverts commit efd641ffab34e433a8d8a7d78914576f2425aa90.

This changeset seems to be needed to suppress a warning on Ubuntu 20.04
https://rubyci.org/logs/rubyci.s3.amazonaws.com/ubuntu/ruby-master/log/20200304T033004Z.log.html.gz
```
closure.c:264:5: warning: 'ffi_prep_closure' is deprecated: use ffi_prep_closure_loc instead [-Wdeprecated-declarations]
  264 |     result = ffi_prep_closure(pcl, cif, callback, (void *)self);
      |     ^~~~~~
```

I guess there was a reason why the commit was reverted (maybe some CIs
failed?), so try it again.

This reverts commit ce6caade7c57a505f73086ccd7b33c14f7715f22.

* Use ffi_closure_free unconditionally.

The current conditionals reflect historic heritage of FFI. Usage of
ffi_closure_free should be better default nowadays, because libffi 3.0.5
fixing issues of ffi_closure_free should be widely available.

* RUBY_LIBFFI_MODVERSION is not used anymore.

Because `ffi_closure_free()` is not used unconditionally, there is no
other use for RUBY_LIBFFI_MODVERSION define, so drop its usage.

* Use more meaningful variable name.

`ver` variable used to be used to pupulate RUBY_LIBFFI_MODVERSION
define. Since the define was removed, the `libffi_dir` variable name
should better describe the remaining usage of the variable.

https://github.com/ruby/fiddle/commit/c49cc79eb8

  * ext/fiddle/closure.c: use directly declaration for standalone gem
    without internal.h.
  * Specify frozen string literal is true.
  * Update gemspec configuration for release version.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59854 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@52988 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

Some external functions I wish to call may take a long time
and unnecessarily block other threads.  This may lead to performance
regressions for fast functions as releasing/acquiring the GVL is not
cheap, but can improve performance for long-running functions
in multi-threaded applications.

This also means we must reacquire the GVL when calling Ruby-defined
callbacks for Fiddle::Closure, meaning we must detect whether the
current thread has the GVL by exporting ruby_thread_has_gvl_p
in internal.h

* ext/fiddle/function.c (struct nogvl_ffi_call_args):
  new struct for GVL release
  (nogvl_ffi_call): new function
  (function_call): adjust for GVL release
  [ruby-core:71642] [Feature #11607]
* ext/fiddle/closure.c (struct callback_args):
  new struct for GVL acquire
  (with_gvl_callback): adjusted original callback function
  (callback): wrapper for conditional GVL acquire
* ext/fiddle/depend: add dependencies
* ext/fiddle/extconf.rb: include top_srcdir for internal.h
* internal.h (ruby_thread_has_gvl_p): expose for fiddle
* vm_core.h (ruby_thread_has_gvl_p): moved to internal.h
* test/fiddle/test_function.rb (test_nogvl_poll): new test

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@52723 b2dd03c8-39d4-4d8f-98ff-823fe69b080e