extmk.rb: build_complete
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@56048 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
extmk.rb: build_complete
under TARGET_SO_DIR and install it only when the gem build
succeeded. [ruby-core:77057] [Bug #12681]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@56048 b2dd03c8-39d4-4d8f-98ff-823fe69b080e