This isn't a direct solution to your problem, but when I worked on a large C++ code base, I found it tremendously helpful to lean more on unit tests as a source of fast feedback for a particular code unit rather than compiling and booting the whole app for a manual test. Manual tests will still be necessary, but they should be less frequent so your long compiles will be less frequent as well.

Even less helpful for you, I recently been able to use Go more frequently, so I have no more long compile times. :p