(toplevel patch) Dependency tidy.

[DJ Delorie]

> The patch to do this is trivial, and just involves putting "gas" before
> "ld" in configure.in:host_tools.

That's what I said.  However, relying on people to maintain that order
is fragile.  It also control the build order when dependencies don't
say otherwise.

I'm ok with relying on the order for convenience, but not as a
replacement for dependencies.  A suitable comment would be needed just
before the list, so that anyone messing with it knows about this.