Following the [JDK-8255796](https://bugs.openjdk.java.net/browse/JDK-8255796)
improvement that ditched the inline contiguous alloc use from Zero, we can now
rely on GC interface to hook the GCs properly. Epsilon GC does not require
anything else. Other GCs require a bit of fiddling and more testing (see e.g.
[JDK-8256497](https://bugs.openjdk.java.net/browse/JDK-8256497)).
Additional testing:
- [x] Linux x86_64 Zero {fastdebug,release}, `gc/epsilon` tests
-------------
Commit messages:
- 8256499: Zero: enable Epsilon GC
Changes: https://git.openjdk.java.net/jdk/pull/1269/files
Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1269&range=00
Issue: https://bugs.openjdk.java.net/browse/JDK-8256499
Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
Patch: https://git.openjdk.java.net/jdk/pull/1269.diff
Fetch: git fetch https://git.openjdk.java.net/jdk pull/1269/head:pull/1269
PR: https://git.openjdk.java.net/jdk/pull/1269
