I'm not sure about generating C++. Please see:
http://xml.apache.org/xalan-j/xsltc_usage.html#api-examples

In that case as long as you code to JAXP interfaces you can decide at
runtime whether to use Xalan-J (with a Translet or a standard 1.0
stylesheet) or Saxon with a 2.0 stylesheet.
If both processors are on the classpath you can set the system
properties to switch between the two.  I guess it comes down to
whether you want to use XSLT 2.0 or not.