Binary builds and workspaces

[Aleksey Shipilev]

Hey,

Even though zgc/zgc forest have no ZGC sources yet, our CI builds it now nevertheless, like it
builds Shenandoah and Epsilon.

This gives us two artifacts:

 *) OpenJDK workspace:
     https://builds.shipilev.net/workspaces/zgc-zgc.tar.xz

   This should be helpful for Europe-residing folks, because cloning the entire monorepo workspace
   would take a while otherwise (>1 hr, by my last measurement). The tarball is rebuilt every night,
   and trivial "hg pull" / "hg up" would bring it to the most up-to-date version. One-liners are in:
     https://builds.shipilev.net/workspaces/README.txt

 *) Binary builds:
     https://builds.shipilev.net/openjdk-zgc/

   x86_64 is built natively, other targets are cross-compiled. Builds are updated every night,
   build frequency might change in future, in both directions. I would try to make build logs
   available too, for easier debugging.

Cheers,
-Aleksey