If your project is a makefile project, just do what François said in the comments.
If you are trying to create a specific configuration, it depends on which version of the CDT you have, as if you could do it.
, . CDT 7.0, , CDT 7.0, . -build App/Config -build App.
(: eclipse CDT 7.0.2, , , - , CDT 8.0 ).