I can say that for C and C++, the compilation is very often parallelized at the translation unit (file) level, by starting multiple instances of the compiler ei

I can say that for C and C++, the compilation is very often parallelized at the translation unit (file) level, by starting multiple instances of the compiler either locally or over a network with something like distcc. This is simple and effective enough that there wouldn't be much gain in parallelizing the compilers: all the cores are already busy most of the time.