http://openjdk.java.net/jeps/283 "Enable GTK 3 on Linux" was included
in OpenJDK 9.
nothing else currently in nixpkgs is using 10, so this just lets us
establish a good baseline as things are ported onto it. if needed,
the build could be parameterized so that any packages that turn out to
need gtk2 could still use it.
* with only one source bundle (per JEP-296), we can use src instead of
srcs, and avoid the need to cd in prePatch
* fetch sources from jdk10u instead of jdk10, to make it easier to
grab updates when they start coming.
* removed commented-out code that became irrelevant in the 8 -> 9
transition (*.pf files, infinality font rendering)
* create jdk10, jre10, and jre10_headless attributes in
all-packages.nix
