Isn't c++ compilation single-threaded and linking multi-threaded? I imagine with pre-compiled headers 64 cores would be a massive overkill. I don't know, if even my 2700x wouldn't be.
C++ compilation is massively multiprocess. Linking is mostly single-process but the gold (for little benefit) and lld (for good benefit) linkers support multithreading.
I am not sure if any c++ compiler can actually compile a single file in parallel but usually you have many small to large files in compiling a project then "make -j" or "ninja" can build in parallel, and it is quite embarrassingly parallel task (but very memory intensive too).
C++ compilers are normally single threaded, so you launch as many instances of the compiler as you can and make them compile different files in parallell
If your code base is 1000+ c/cpp files each of these needs to be compiled into an o file so all of that can be done in parallel.