Added following gemspecs.
* extensions: date, dbm, etc, fiddle, gdbm, sdbm, stringio, strscan, zlib
* pure ruby libraries: cmath, csv, fileutils, scanf, webrick
psych and rdoc is out of scope of this commit. I will merge after
upstream was change to `frozen_string_literal: true`.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59115 b2dd03c8-39d4-4d8f-98ff-823fe69b080e