How to invoke the clang compiler from my clang tool

Question

I have an existing and working source-to-source code modification tool using libtooling (written in C++). Now I want to integrate this tool into clang, so users can compile the modified source code without actually saving it somewhere. The modification part isn't problematic, Matchers + Rewriters work the same way with clang, my problem is how to tell the compiler to reparse the source code after my changes.