Enable building with GCC 10.3 for JDK18 and above on Linux (Excluding OpenJ9)

[sxa]

Can be implemented now that adoptium/infrastructure#2420 has been merged
Fixes #2787 (Although for now not including JDK17)

[karianna]

Couple of small whitespace suggestions. Failed GH Actions will need checking as well.

[karianna]

The GH Actions failing will still need to be addressed and the ECA check?

[sxa]

Failing actions were because the adoptopenjdk/centos7_build_image does not appear to have been updated with the latest playbook changes (The production centos6_build_image used on x64 builds looks ok). Having said that, I've adjusted the code so it will back off to GCC 7 instead of 4.8 when 10 does not exist, which should pass the checks, but we need to look into why we're running the checks against a docker build image we're not using, and why it's not getting the updates since it may be out of date in other ways too if it hasn't got this latest change.

@gdams any idea why the centos7 one may not have got the update from adoptium/infrastructure#2420

[sxa]

@karianna Bisheng11 seems to be broken in other PRs so that check failing is probably not a blocker
It has also been failing in the nightly builds so this is not a blocker for the PR.

[gdams]

@gdams any idea why the centos7 one may not have got the update from adoptium/infrastructure#2420

@sxa looks like the playbook updater has been failing in Jenkins for some time: https://ci.adoptopenjdk.net/view/Infra/job/centos7_docker_image_updater/. Weirdly it seems to be failing to push (I'll do some digging)

[sxa]

@gdams any idea why the centos7 one may not have got the update from adoptium/infrastructure#2420

@sxa looks like the playbook updater has been failing in Jenkins for some time: https://ci.adoptopenjdk.net/view/Infra/job/centos7_docker_image_updater/. Weirdly it seems to be failing to push (I'll do some digging)

Let's move further discussion into adoptium/infrastructure#2432

[sxa]

I'm comfortable that this is having the desired effect - merging now.