Update config.guess to the version from autoconf 2.72

[waywardmonkeys]

Fixes #281. Identification of newer systems such as macOS on Apple Silicon was not working correctly with the old version of this file.

[rptb1]

Executing proc.review.express.

1. Start time 14:24.
2. Source documents available (via Wayback, since gnu.org is down): GNU Autoconf manual.
3. Applied entry.universal and entry.impl. Entry passed.
4. Called in @thejayps to the review.
5. @thejayps agrees this is a low risk change and that express review is appropriate.
6. Commencing checking...

[rptb1]

Executing proc.review.check:

1. Start time 14:34.
2. Fetched the PR branch to Kiwi-Ubuntu (Ubuntu 22.04) and ran autoconf, autoreconf, configure, make, etc. with success.
3. Followed auxillary files instructions from the Autoconf manual to fetch https://git.savannah.gnu.org/cgit/config.git/plain/config.guess and compared that with this change. Minor differences only.
4. The above instructions imply that updating config.guess alone is OK. See discussion following Update to autotools 2.72 #289 (comment) .
5. I note that on this PR, the automated tests on macos-latest have passed, though the logs have gone.
6. Finished checking at 14:45.

[rptb1]

I note that GitHub's "macos-latest" runner is now on M1 hardware which makes a lot of this easier. We can likely decommission the Mac we were using for this purpose at Ravenbrook (see also #229 ).

[rptb1]

Executing proc.review.express.brainstorm:

1. We should investigate how we can trigger builds at intervals so that we get early warnings of platform changes even when there is not much activity in the MPS repository. This seems to be possible via a "schedule" in the workflow.

[rptb1]

Executing proc.review.exit:

1. Start time 15:01.
2. Escalated Changes in the build environment are not caught until there's a change in the MPS #294 .
3. Change passed.

[rptb1]

proc.review.exit.pass

[thejayps]

Executing proc.merge.pull-request

1. Start time 15:17.
2. Actually attempting a merge following the proc.merge.pull-request in another as yet un-reviewed branch which removes the dependency on perforce
3. Checklist questions: 2: we're pretty sure it does. 8. Work comes from GNU, but config.guess has a special licence
4. End time 1537 - merge took 20 mins