In case someone other than me has failed their perception check, note that makepanda has a --threads option. Posting this here just to make it easy to find by a web search.
Using --threads 8 speeded up a full build from 45 minutes to 7 minutes (speedup factor 6.43) on my AMD FX-8150. Just make sure you have enough RAM.
It says so right there in the help text when you run python makepanda/makepanda.py without parameters, but although I had browsed through that help, I hadn’t noticed makepanda has the ability to run in parallel.
Found this tip from an old thread (2008): Precompiled headers
(Also, the help text for the --threads option mentions “see the manual”, but neither doc/INSTALL-MK nor the online manual says anything about this option.)