RFR: 7526: JMC not buildable with jdk17 [v2]

[Johannes Bechberger]

On Mon, 17 Jan 2022 17:16:54 GMT, Johannes Bechberger <duke at openjdk.java.net> wrote:

>> Tested on Java 11 x86 and aarch64 (azul, but only builds), and on Java 17 x86 and aarch64.
>
> Johannes Bechberger has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix maven cache directories in GitHub actions

This PR has currently a few issues (that I'm dealing with in the next few) days:
- [ ] fix reliance on `tools.jar` (work with tycho to open up modules)
- [ ] improve GitHub actions
- [ ] fix spurious bug related to JDP that only happens sometimes
- [ ] fix bug that is probably related to trying to build this on an Mac M1

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PR: https://git.openjdk.java.net/jmc/pull/363