RFR: Enable 1-step workflow with Shenandoah GC

[Aleksey Shipilev]

WIP, includes upstream [JDK-8293650](https://bugs.openjdk.org/browse/JDK-8293650).

I checked this works well:


#!/bin/bash
make images
J=build/macosx-aarch64-server-fastdebug/images/jdk/bin/java
rm -fv JavacBenchApp.cds*
$J -XX:+UseShenandoahGC -XX:CacheDataStore=JavacBenchApp.cds -cp JavacBenchApp.jar JavacBenchApp 50
$J -XX:+UseShenandoahGC -XX:CacheDataStore=JavacBenchApp.cds -cp JavacBenchApp.jar JavacBenchApp 50


I'll look around what other tests I need to run.

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Commit messages:
 - Temporary drop the alignment, so that tests work
 - Shenandoah support

Changes: https://git.openjdk.org/leyden/pull/8/files
  Webrev: https://webrevs.openjdk.org/?repo=leyden&pr=8&range=00
  Stats: 48 lines in 7 files changed: 33 ins; 1 del; 14 mod
  Patch: https://git.openjdk.org/leyden/pull/8.diff
  Fetch: git fetch https://git.openjdk.org/leyden.git pull/8/head:pull/8

PR: https://git.openjdk.org/leyden/pull/8