common.mk: no purelib
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@37719 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
common.mk: no purelib
since r28841, so set to an empty list to get rid of a bogus path in
child processes, which caused an insecure operation exception in
test/ruby/test_encoding.rb:test_unsafe.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@37719 b2dd03c8-39d4-4d8f-98ff-823fe69b080e