"Concatenated" builds seem to be the best band-aid for this. Concatenate as many source files as possible before compiling, #include a bunch of cpp files into one big file. It makes tracking down errors slightly harder and macros a bit more risky, but greatly improves the overall build efficiency.
It's a balance, but on many projects the overhead of the headers themselves is so large that concatenating a few .cpp files together doesn't increase incremental compilation time significantly over simply building each .cpp file in isolation.
Incremental compilation opportunities are rarer than we'd like on C++: as soon as you add a new class member or function, that's potentially a huge recompile.
