def build_dir(src_dir, obj_dir)
      if src_dir.is_a?(String)
        src_dir = src_dir.gsub("\\", "/").sub(%r{/*$}, "")
      end
      @build_dirs.unshift([src_dir, obj_dir])
    end
def build_dir(src_dir, obj_dir)
      if src_dir.is_a?(String)
        src_dir = src_dir.gsub("\\", "/").sub(%r{/*$}, "")
      end
      @build_dirs.unshift([src_dir, obj_dir])
    end
Specify a build directory for this Environment.

 Source files from src_dir will produce object files under obj_dir.

 @param src_dir [String, Regexp]
   Path to the source directory. If a Regexp is given, it will be matched
   to source file names.
 @param obj_dir [String]
   Path to the object directory. If a Regexp is given as src_dir, then
   obj_dir can contain backreferences to groups matched from the source
   file name.

 @return [void]