broken utf-8

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41786 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* lib/mkmf.rb (CONFIG['CPPOUTFILE']): fix r41769; CONFIG['CPPOUTFILE']
  may be nil.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41787 b2dd03c8-39d4-4d8f-98ff-823fe69b080e