Compiling Chromium, the biggest C++ project I know, takes on the order of 8 hours with a somewhat old but quite powerful server. Linking Chromium on my laptop, with 8GB of RAM, required me to increase my swap space from 8GB to 16GB.
Going away from C's linker and header file-model, which really doesn't work well for C++, to something based on a proper module system, would be amazing.