[InterNetNews/inn] 4ed022: Build concurrency fixes

[Richard Kettlewell]

  Branch: refs/heads/2.6
  Home:   https://github.com/InterNetNews/inn
  Commit: 4ed0228d8fc832e41eb2b1583d17b669cab71634
      https://github.com/InterNetNews/inn/commit/4ed0228d8fc832e41eb2b1583d17b669cab71634
  Author: Richard Kettlewell <rjk at greenend.org.uk>
  Date:   2021-10-31 (Sun, 31 Oct 2021)

  Changed paths:
    M Makefile

  Log Message:
  -----------
  Build concurrency fixes

We serialize build of top-level subdirectories.  The previous attempt
to support make -j was broken, since the subdirectories have dependencies
between them and attempt to cross-invoke one another, leading to multiple
concurrent make invocations on the same directory.

A couple of missing dependencies are also added.  The sql-init.h
dependency should be generated by makedepend, but it's confused about
object code extensions.  This change is a stopgap until that is
addressed.