Serialization dependencies muck up configure-on-demand

[DJ Delorie]

> Do we need the serialization dependencies?

We need to make sure that no two configures run at the same time.  If
you can figure out a better way to do that, please do.

> While we support all sorts of versions of Make, do we actually
> support parallel make on anything that doesn't recognize
> .NOTPARALLEL?

We want to run the toplevel makefile in parallel, because we want to
do the builds and tests in parallel.  So, we want to get rid of
.NOTPARALLEL, not depend on it.