8337265: [Graal] Add basic libgraal GitHub Actions job

[dougxc]

Since libgraal is built with SVM and SVM is closely tied to OpenJDK internals, it's easy enough for an OpenJDK change to break building libgraal.
This PR adds a GitHub Actions job that does a basic build and test of libgraal by pulling sources from the graal repo.
The job always exits with success but if libgraal building or testing fails, a comment is added to head commit of the PR that triggers a notification to be sent to the Graal compiler team.
The comment makes it clear that no further action is needed by the PR author.

Example comment: dougxc@b567ab9#commitcomment-144869332

---

Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
• Change must not contain extraneous whitespace
• Commit message must refer to an issue

Integration blocker

 ⚠️ Title mismatch between PR and JBS for issue JDK-8337265

Issue

• JDK-8337265: Test static-libs build in GitHub Actions (Enhancement - P4) ⚠️ Title mismatch between PR and JBS. ⚠️ Issue is already resolved. Consider making this a "backport pull request" by setting the PR title to Backport <hash> with the hash of the original commit. See Backports.

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/20347/head:pull/20347
$ git checkout pull/20347

Update a local copy of the PR:
$ git checkout pull/20347
$ git pull https://git.openjdk.org/jdk.git pull/20347/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 20347

View PR using the GUI difftool:
$ git pr show -t 20347

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/20347.diff

[bridgekeeper]

👋 Welcome back dnsimon! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

❗ This change is not yet ready to be integrated.
See the Progress checklist in the description for automated requirements.

[openjdk]

@dougxc The following label will be automatically applied to this pull request:

• build

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

[bridgekeeper]

@dougxc This pull request has been inactive for more than 8 weeks and will be automatically closed if another 8 weeks passes without any activity. To avoid this, simply add a new comment to the pull request. Feel free to ask for assistance if you need help with progressing this pull request towards integration!