tools: let toolchain repo build libbfd.

[glguida]

We should add the gcc toolchain as a submodule. (back to the original mh).

Toolchain should build libbfd (and the other binutils libraries) for objappend.

This will ensure we only have one version of binutils, and we can build the required libraries from only one version.

And will clean up the bootstrapping process for building nux.

[glguida]

Alternatively, rewrite objappend to not require libbfd.