Provide `gem.build_complete` file for binary gems.
    
    When the `gem.build_complete` file is not present, Bundler treats the
    package as uninstalled, therefore leaves it out from the dependency
    resolution with error such as:
    
    ~~~
    Could not find gem 'openssl', which is required by gem 'net-ssh', in any of the sources.
    ~~~
    
    [1] https://github.com/rubygems/rubygems/blob/1969e8adfc714d5fc3689e6de0689b4c7b3e7f0d/bundler/lib/bundler/source/rubygems.rb#L353-L384