RFR: 8288195: Prepare build system for GHA changes

[Magnus Ihse Bursie]

A few changes to the build system is needed for the GHA rewrite ([JDK-8287906](https://bugs.openjdk.org/browse/JDK-8287906)).

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Commit messages:
 - 8288195: Prepare build system for GHA changes

Changes: https://git.openjdk.org/jdk/pull/9122/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=9122&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8288195
  Stats: 28 lines in 3 files changed: 13 ins; 0 del; 15 mod
  Patch: https://git.openjdk.org/jdk/pull/9122.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9122/head:pull/9122

PR: https://git.openjdk.org/jdk/pull/9122