This makes several adjustments around what is linked into JRE.
* system giflib, libjpeg, zlib are now used unconditionally;
* libstdc++ is linked dynamically.
For full version:
* GTK+ and GNOME libraries are linked;
* Extra X11 libraries are linked;
* CUPS is linked;
* libmagic (file) is linked.
For minimal version:
* All X11 support is removed;
* Sound support is removed.
* Fonts and their support are not lined.
jre8_headless is added as a minimal build.
Overall this adds support for all things GUI into the default Java build and
removes them from the minimal build.
* openjdk: Keep {include,man} in $out/lib/opendjk.
This is a standard layout that some JDK consumers expect.
* openjdk/8: Improve clarity of some symlink commands with terminating slash.
The most complex problems were from dealing with switches reverted in
the meantime (gcc5, gmp6, ncurses6).
It's likely that darwin is (still) broken nontrivially.
