In a "merged-usr" system, `/lib` is a symlink to `/usr/lib`. When
installing *sys-apps/systemd*, Portage checks to ensure this is the
case. If this happens after `make modules_install` is run, `/lib` is
a directory, which causes the installation to fail. To avoid this, we
need to explicitly install the modules into `/usr/lib` so that the
symlink can be created later.
Building the OS is now as simple as running `make` on a Gentoo system.
Interestingly, when `make` is executed as a (grand)child process of
another `make` process, it always prints an `Entering directory ...`
message. This breaks the `make kernelversion` command, by adding
extraneous text to the output.