RFR: 8256393: Github Actions build on Linux should define OS and GCC versions

[Aleksey Shipilev]

On Mon, 16 Nov 2020 13:36:57 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> We should be more explicit about OS and compiler versions used in the GitHub Actions builds, to avoid problems caused by unexpected changes to the defaults. This patch changes the OS and GCC versions used from ubuntu-latest (currently 18.04, but will change to 20.04 sometime soon) / default (currently 9.3.0) to 20.04 / 10.2.0.
>
> Marked as reviewed by shade (Reviewer).

> Right, currently ubuntu-latest means 18.04, but that is only true for another two weeks (see [actions/virtual-environments#1816](https://github.com/actions/virtual-environments/issues/1816) - originally it was also planned for next week). So I think we should go straight for the upcoming latest.

All right, changing this today makes sense to me.

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PR: https://git.openjdk.java.net/jdk/pull/1225