Going back to October of 2013 has been work on this GCC-based embeddable JIT compiler that initially generated a lot of interest but has yet to be incorporated into a stable GNU Compiler Collection release.
At the recent GNU Tools Cauldron 2014 in Cambridge, there was a presentation and more discussion around libgccjit. David Malcom of Red Hat has been the one leading the GCC JIT endeavor and presented on it at the annual GNU/GCC event. For those interested his presentation slides are available here.
David Malcom wrote the Coconut compiler as an example Python JIT compiler using the new GCC interfaces, which compiles CPython bytecode into machine code and uses libgccjit's Python bindings. Malcom is hopeful bindings for other languages to libgccjit will be added going forward. Besides Coconut there's also been other experimental method JITs implemented against this GCC JIT shared library but not yet any tracing JITs.
While the code hasn't yet been merged, it's already been beneficial to GCC in finding various issues within GCC as a result of these new operations. David Malcom is encouraging distribution vendors to begin packaging libgccjit, developers to try it for their language runtimes and to hook in more language bindings, and ultimately for the work to be incorporated into the next major GCC release. Right now it's looking like the next GNU Compiler Collection release will be the release of GCC 5.0 in 2015.