Gem::VersionOption#add_platform_option

# File tmp/rubies/ruby-3.3.0/lib/rubygems/version_option.rb, line 18
def add_platform_option(task = command, *wrap)
  Gem::OptionParser.accept Gem::Platform do |value|
    if value == Gem::Platform::RUBY
      value
    else
      Gem::Platform.new value
    end
  end

  add_option("--platform PLATFORM", Gem::Platform,
             "Specify the platform of gem to #{task}", *wrap) do |value, options|
    unless options[:added_platform]
      Gem.platforms = [Gem::Platform::RUBY]
      options[:added_platform] = true
    end

    Gem.platforms << value unless Gem.platforms.include? value
  end
end