platform

when doing a bundle installation or a bundle update, one gets this when compiling platform on f29:

...
Fetching scrypt 3.0.6 (was 3.0.5)
Installing scrypt 3.0.6 (was 3.0.5) with native extensions
Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

    current directory: /tmp/bundler20181101-17194-1w4odu6scrypt-3.0.6/gems/scrypt-3.0.6/ext/scrypt
/usr/bin/ruby -rrubygems /usr/share/gems/gems/rake-12.3.1/exe/rake RUBYARCHDIR=/tmp/bundler20181101-17194-1w4odu6scrypt-3.0.6/extensions/x86_64-linux/2.5.0/scrypt-3.0.6
RUBYLIBDIR=/tmp/bundler20181101-17194-1w4odu6scrypt-3.0.6/extensions/x86_64-linux/2.5.0/scrypt-3.0.6
Ignoring ffi-1.9.25 because its extensions are not built. Try: gem pristine ffi --version 1.9.25
Ignoring ffi-1.9.23 because its extensions are not built. Try: gem pristine ffi --version 1.9.23
Ignoring nio4r-2.3.1 because its extensions are not built. Try: gem pristine nio4r --version 2.3.1
Ignoring nokogiri-1.8.5 because its extensions are not built. Try: gem pristine nokogiri --version 1.8.5
Ignoring nokogiri-1.8.2 because its extensions are not built. Try: gem pristine nokogiri --version 1.8.2
Ignoring websocket-driver-0.6.5 because its extensions are not built. Try: gem pristine websocket-driver --version 0.6.5
rake aborted!
LoadError: cannot load such file -- ffi
/usr/share/gems/gems/ffi-compiler-1.0.1/lib/ffi-compiler/compile_task.rb:4:in `<top (required)>'
/tmp/bundler20181101-17194-1w4odu6scrypt-3.0.6/gems/scrypt-3.0.6/ext/scrypt/Rakefile:1:in `<top (required)>'
/usr/share/gems/gems/rake-12.3.1/exe/rake:27:in `<main>'

Caused by:
LoadError: cannot load such file -- ffi-compiler/compile_task
/tmp/bundler20181101-17194-1w4odu6scrypt-3.0.6/gems/scrypt-3.0.6/ext/scrypt/Rakefile:1:in `<top (required)>'
/usr/share/gems/gems/rake-12.3.1/exe/rake:27:in `<main>'
(See full trace by running task with --trace)

rake failed, exit code 1

Gem files will remain installed in /tmp/bundler20181101-17194-1w4odu6scrypt-3.0.6/gems/scrypt-3.0.6 for inspection.
Results logged to /tmp/bundler20181101-17194-1w4odu6scrypt-3.0.6/extensions/x86_64-linux/2.5.0/scrypt-3.0.6/gem_make.out

An error occurred while installing scrypt (3.0.6), and Bundler cannot continue.
Make sure that `gem install scrypt -v '3.0.6'` succeeds before bundling.

In Gemfile:
  authlogic was resolved to 4.4.2, which depends on
    scrypt