[blasdel]

Gentoo avoids making patches specific to itself wherever possible, when it does it's generally just to make it compile+work, the changes are straightforward, and they are applied live on your machine in a self-documenting way.

The build process is also sophisticated enough to be able to 'slot' potentially-incompatible versions of the same package so that they can be installed simultaneously. From my recent snapshot of the package repo I can install 5 different simultaneous major versions of postgres, with a variety of independent build options.