This splits the current bootstrap stage into two stages:
A bootstrap stage, which like today, a reference is checked into the
tree. It just builds the "core" blueprint binaries -- minibp,
gotestmain, and choosestage. Just enough to build the next stage's ninja
file.
A primary builder stage. This builds the primary builder, the main ninja
file, and any other bootstrap binaries (bpfmt, etc).
The main advantage here is that the checked in file really only contains
references to blueprint -- not the primary builder. This will allow us
to make the primary builder more dynamic, by loading more module types
that may or may not exist in all trees.
It's even possible to reuse the build.ninja.in in the blueprint repo
directly now. We don't currently do that, since we still want to turn on
tests.
Change-Id: I18683891ed7348b0d7af93084e3a68a04fbd5dbc
efd2de734d