RFR: ZGC support for loom

[Erik Österlund]

This pull request adds the appropriate code required to get loom working with ZGC.

-------------

Commit messages:
 - ZGC support for loom

Changes: https://git.openjdk.java.net/loom/pull/14/files
 Webrev: https://webrevs.openjdk.java.net/loom/14/webrev.00
  Stats: 127 lines in 27 files changed: 79 ins; 14 del; 34 mod
  Patch: https://git.openjdk.java.net/loom/pull/14.diff
  Fetch: git fetch https://git.openjdk.java.net/loom pull/14/head:pull/14

PR: https://git.openjdk.java.net/loom/pull/14