infrastructure: switch to package checks of libraries

[Marc Espie <espie_(_at_)_nerim_(_dot_)_net>]

I've finally removed the old src scaffolding for lib-depends-check, and
switched us to newlib-depends checks on packages.

- matches the semantics of the current pkg_add infrastructure.
- solves all multi packages issue, since we no longer look directly
at fake.

This will change some habits. Since lib-depends-check now requires
binary package, people writing initial list of dependencies will need
to iterate through

make lib-depends-check
[edit Makefile]
make clean=packages   (new added step).

Also, lib-depends-check now only checks what it needs to check, namely that
there exists @wantlib  markers for all libraries external to the package.

Walking down dependency lists requires dependent packages to be present.
It also does not need any extra code, since pkg_add already does all the
checking, so using pkg_add -n on the binary packages will be enough.

The a.out handling code is actually untested.


I would like to thank Alek for all the hard work he's put into upgrading
all our ports to have mostly correct WANTLIB.