* enc/Makefile.in: became a serb template.
* enc/make_encmake.rb: creates enc.mk from enc/Makefile.in using serb.
* lib/mkmf.rb (relative_from): moved from ext/extmk.rb.
* lib/mkmf.rb ($extmk): true if under to top source directory, not
only ext.
* lib/mkmf.rb (depend_rules): extracted from create_makefile.
* tool/serb.rb (serb): splitted from tool/compile_prelude.rb.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@14267 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
nobu