title: Can't Install ffi -v '1.9.18' on macos Catalina
body: <p>Can't install specific ffi version. If I run gem install ffi, everything works just fine but I need specific version 1.9.18 and it doesn't work.</p>
  <pre><code>Fetching ffi 1.9.18
  Installing ffi 1.9.18 with native extensions
  Gem::Ext::BuildError: ERROR: Failed to build gem native extension.
  
  current directory: /Users/chille/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/ffi- 
  1.9.18/ext/ffi_c
  /Users/chille/.rbenv/versions/2.6.5/bin/ruby -I 
  /Users/chille/.rbenv/versions/2.6.5/lib/ruby/2.6.0 -r
  ./siteconf20200928-22154-72wopi.rb extconf.rb
  checking for ffi_call() in -lffi... yes
  checking for ffi_prep_closure()... yes
  checking for ffi_raw_call()... yes
  checking for ffi_prep_raw_closure()... yes
  checking for shlwapi.h... no
  checking for rb_thread_blocking_region()... no
  checking for rb_thread_call_with_gvl()... yes
  checking for rb_thread_call_without_gvl()... yes
  checking for ffi_prep_cif_var()... yes
  creating extconf.h
  creating Makefile
  
  current directory: /Users/chille/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/ffi- 
  1.9.18/ext/ffi_c
  make &quot;DESTDIR=&quot; clean
  
  current directory: /Users/chille/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/ffi- 
  1.9.18/ext/ffi_c
  make &quot;DESTDIR=&quot;
  compiling AbstractMemory.c
  compiling ArrayType.c
  compiling Buffer.c
  compiling Call.c
  Call.c:355:5: error: implicit declaration of function 'rb_thread_call_without_gvl' is 
  invalid in C99
  [-Werror,-Wimplicit-function-declaration]
  rbffi_thread_blocking_region(call_blocking_function, data, (void *) -1, NULL);
  ^
  ./Thread.h:78:39: note: expanded from macro 'rbffi_thread_blocking_region'
  # define rbffi_thread_blocking_region rb_thread_call_without_gvl
                                    ^
  1 error generated.
  make: *** [Call.o] Error 1
  
  make failed, exit code 2
  
  Gem files will remain installed in 
  </code></pre>
  <p>/Users/chille/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/ffi-1.9.18 for inspection.
  Results logged to /Users/chille/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/extensions/x86_64-
  darwin-19/2.6.0/ffi-1.9.18/gem_make.out</p>
  <p>An error occurred while installing ffi (1.9.18), and Bundler cannot continue.
  Make sure that <code>gem install ffi -v '1.9.18'</code> succeeds before bundling.</p>
  <p>In Gemfile:
  bootstrap-sass was resolved to 3.3.7, which depends on
  sass was resolved to 3.5.5, which depends on
  sass-listen was resolved to 4.0.0, which depends on
  rb-inotify was resolved to 0.9.10, which depends on
  ffi</p>