When migrating the manual to the top-level, the include order was
sorted by name of the subdir. But this changed the chapter order
of the manual in the process. Change the sorting back to match
existing chapters and update the comments to explain.
Make sure we depend on the right name of mkdoc all the time, and that
the rules that need it (e.g. .def files) depend on it.
Reported-by: Jon Turney <jon.turney@dronecode.org.uk>
This allows building the libc & libm pages in parallel, and drops
the duplication in the subdirs with the chew/chapter settings.
The unused rules in Makefile.shared are left in place to minimize
noise in the change.
This doesn't migrate all the docs, just the libc's manual (pdf/info).
This is to show the basic form of migrating the chew files.
For subdirs that didn't have any docs, I've stripped their settings
for clarity. If someone wanted to suddenly add docs, they can add
the corresponding Makefile.inc files easily.