handle external/ libs that we also have ebuilds for

Since we have a bunch of libs already in external/, make sure we stub
out all the ebuilds that duplicate things.  This way we don't build
from two different sources and clobber things in weird ways.

In order for packages to find their headers though, we need to set up
a system include tree for packages that aren't "installed".


Change-Id: Idb5a4711dd30f9c5011dda8d06a874849a3609cb
4 files changed