Since I started touching this subsystem, I found the name confusing
since this is the part where we actually compile the kernel and we have
a ready-to-use configuration.
The stated goal of the commit introducing it[1] is to provide a function
to
> make it possible to build a kernel with a user provided .config.
Considering that this is supposed to be a differentiation from other
build mechanisms and nowadays this is the only way to build kernels in
nixpkgs, I figured that `build.nix` is a better name.
`pkgs.linuxManualConfig` isn't renamed on purpose: Kloenk and I are
planning to do more involved work and it may become necessary to change
parts of the API. So asking users to do a migration now just to add
another one soon isn't worth it.
[1] bf7467cbb1
1965f3c77d