# File lib/mkrf/availability.rb, line 98
    def has_header?(header, *paths)
      if header_already_loaded?(header) || header_can_link?(header) || 
                     header_found_in_paths?(header, paths)
        defines << format("HAVE_%s", header.tr("a-z./\055", "A-Z___"))
        return true 
      end
      
      logger.warn "Header not found: #{header}"
      return false
    end