common.mk: use BASERUBY
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43888 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
common.mk: use BASERUBY
BASERUBY since r43617. [ruby-dev:47823] [Bug #9169]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43888 b2dd03c8-39d4-4d8f-98ff-823fe69b080e