# File lib/mkmf.rb, line 657
def have_func(func, headers = nil, &b)
  checking_for checking_message("#{func}()", headers) do
    if try_func(func, $libs, headers, &b)
      $defs.push(format("-DHAVE_%s", func.upcase))
      true
    else
      false
    end
  end
end