openjdk8: rework dependencies

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.