Gem.win_platform?

# File tmp/rubies/ruby-3.3.0/lib/rubygems.rb, line 992
def self.win_platform?
  if @@win_platform.nil?
    ruby_platform = RbConfig::CONFIG["host_os"]
    @@win_platform = !WIN_PATTERNS.find {|r| ruby_platform =~ r }.nil?
  end

  @@win_platform
end