Does Chromium have `make -j$(nproc)` or equivalent? Because a few hours on a fairly recent processor with a whole bunch of cores sounds long.
Despite that, it takes 4-8 hours to compile, due to two factors: 40,000+ separate targets, of which most are C++ files (famously slow to compile anyway).
And yes, 40,000+ separate targets is no exaggeration; ninja's first run claims about 18,000 targets, and after it finishes those, it generates a second ninja file that has to compile 23,000 targets.
I personally think it's worth it. Others may disagree, and I can't blame them. I have to run it overnight.
EDIT: Looks like popularity is on the rise [1]. Hopefully it will make it into the community repository.
[1] https://pkgstats.archlinux.de/packages/ungoogled-chromium
It is really hard to keep up-to-date with security patches if you need to compile every few days from source with that time..
Edit: Also 32GB RAM which matters
Edit: Also, 3900 is 3900X running on eco mode (same spec but half power). You might get a lot more performance by tuning BIOS settings.
I'll take a peek at the BIOS, but I'll also no good at doing such things.
I wonder how it compares to the build time of something with equivalent functionality, like firefox.