Traditionally, the Gentoo package manager didn't actually compile the Linux kernel at all. Instead it just extracted the source code to a folder on your hard drive and you were supposed to go configure, build, and install it yourself. Gentoo Wiki pages would list out the options you had to go set in the `make menuconfig` menu to get specific software to work.

These days there is a package that builds the kernel for you, but it relies on the "savedconfig" system to just save/load the entire kernel config file instead of using USE flags. So you still have to root around in the config menu yourself to change things.

In my experience Linux is very good at correctly declaring dependencies between options, and still working with options disabled, so this isn't as much of a problem as it seems to be for Chromium.