RFR: 8313707: GHA: Bootstrap sysroots with --variant=minbase

[Fei Yang]

On Thu, 3 Aug 2023 16:14:06 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> We don't need the fully bootable Debian installation to build against. Therefore, we can bootstrap with `--variant=minbase`. The sysroots are about 5..10% smaller then.
> 
> This would also make our builds more immune to issues like [JDK-8313701](https://bugs.openjdk.org/browse/JDK-8313701). Note how RISC-V GHAs are fixed with this PR by dodging the systemd dependency failure.
> 
> Additional testing:
>  - [x] GHA cross-compilation builds

Looks reasonable to me (Not a build expert). Thanks.

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

Marked as reviewed by fyang (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/15140#pullrequestreview-1562462320