nokogiri_find_header (ext/nokogiri/extconf.rb)

    # File ext/nokogiri/extconf.rb, line 76
    def nokogiri_find_header header_file, *paths
      message = checking_message(header_file, paths)
      header = cpp_include header_file
      checking_for message do
        found = false
        paths.each do |dir|
          if File.exists?(File.join(dir, header_file))
            opt = "-I#{dir}".quote
            if try_cpp header, opt
              unless CUSTOM_DASH_I.include? dir
                $INCFLAGS = "#{opt} #{$INCFLAGS}"
                CUSTOM_DASH_I << dir
              end
              found = dir
              break
            end
          end
        end
        found ||= try_cpp(header)
      end
    end