* ext/extmk.rb (extract_makefile, extmake, configuration): store
  extra libraries to be installed.
* tool/rbinstall.rb (ext-arch): install extra libraries.
* ext/zlib/extconf.rb: install zlib if built.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@56230 b2dd03c8-39d4-4d8f-98ff-823fe69b080e