Fallback to using uname machine for hosts using uutils/coreutils

[alavaliant]

Short description

Set the uname resolver to fallback to using the uname machine value to replace uname processor. If the uutils/coreutils version of uname is being used (which returns unknown for uname -p). This fixes various facts like processor.extensions and processor.isa on Distributions like Ubuntu 26.04 which use uutils/coreutils by default.

(This PR follows on from #97 which I accidentally caused to be automatically closed while trying to fix my commit to be signed )

Checklist

I have:

• [* ] read the CONTRIBUTING.md document
• [ *] read and accepted the Developer Certificate of Origin document and added a Signed-off-by annotation to each of my commits
• [ *] tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)

[alavaliant]

Sorry for the accidental duplication of the PR, but as far as I can verify the signing state of the commit is now correct. rubocop passes and the change to the code looks correct. So this PR hopefully shouldn't require any further changes to be in a state where it can be merged.