RFR: 8357979: Compile jdk.internal.vm.ci targeting the Boot JDK version

[Magnus Ihse Bursie]

>From the bug description:

There are plans to build libgraal in JDK master using a version of Native Image running on a JDK one version behind JDK master. This Native Image execution needs to be able to load the JVMCI classes as they are built into the libgraal image. As such, the JVMCI classes must have a class file major version of N-1 where N is the major class file version of JDK master. 

This PR is basically the same change as published by Doug in https://github.com/openjdk/jdk/pull/25494, but it contains some cleanup and adds and uses the `TARGET_RELEASE` argument that Doug correctly realized was needed.

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

Commit messages:
 - 8357979: Compile jdk.internal.vm.ci targeting the Boot JDK version

Changes: https://git.openjdk.org/jdk/pull/26069/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26069&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8357979
  Stats: 12 lines in 5 files changed: 4 ins; 3 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/26069.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26069/head:pull/26069

PR: https://git.openjdk.org/jdk/pull/26069