Add platform triplets for x86_64 GNU/Hurd

[sthibaul]

Bug report

Checklist

• I am confident this is a bug in CPython, not a bug in a third-party project
• I have searched the CPython issue tracker,
  and am confident this bug has not been reported before

CPython versions tested on:

CPython main branch

Operating systems tested on:

Other

Output from running 'python -VV' on the command line:

N/A

A clear and concise description of the bug:

Building on x86_64 GNU/Hurd fails with

Misc/platform_triplet.c:260 error: #error unknown platform triplet

Trivial patch posted to #108045

Linked PRs

• gh-108447: Add support for x86_64 on GNU/Hurd #108045
• [3.12] gh-108447: Detect platform triplets for x86_64 GNU/Hurd (GH-108045) #111987
• [3.11] gh-108447: Detect platform triplets for x86_64 GNU/Hurd (GH-108045) #111988

[erlend-aasland]

Restyled as a feature.