At some point when you build LLVM.with the default options, you hit a moment where most of what's left to do is linking a number of executables, all statically

At some point when you build LLVM.with the default options, you hit a moment where most of what's left to do is linking a number of executables, all statically linking libllvm.a. They are all relatively slow to link, and there aren't enough of them to fill 32 or 64 cores. And they require a lot of RAM, so if you don't have enough RAM, you might end up swapping too.