The article mentions debug build time as a legitimate pain point about the LLVM project. General good advice, which unfortunately isn't enabled by default: use dynamic linking, make sure you're using lld, enable split dwarfs (and -Wl,--gdb-index for faster gdb load times!), enable optimized tablegen[0]. ccache doesn't hurt but isn't actually such a big benefit unless you switch between branches a lot.

Oh, and buy a Threadripper. Seriously, you won't regret it.

[0] TableGen is LLVM's internal DSL swiss army knife. You can separately enable optimizations for TableGen independently of optimizations in the resulting LLVM builds, which you should basically always do unless you're working on TableGen itself.