Add initial support for hppa-unknown-linux-gnu

[hdeller]

This is the followup pull-request from:
#3032

[rustbot]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @JohnTitor (or someone else) soon.

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[JohnTitor]

Thanks! Overall LGTM with one comment

[JohnTitor]

@bors r+

[bors]

📌 Commit 386afa6 has been approved by JohnTitor

It is now in the queue for this repository.

[bors]

⌛ Testing commit 386afa6 with merge d361e08...

[bors]

☀️ Test successful - checks-actions, checks-cirrus-freebsd-13, checks-cirrus-freebsd-14
Approved by: JohnTitor
Pushing d361e08 to main...

[bors]

👀 Test was successful, but fast-forwarding failed: 422 Changes must be made through the merge queue

[glaubitz]

I guess, we could start sending such PRs for alpha and sh4 as well. No need to do it for ia64 which has already been removed from the kernel and glibc as it's on its way out.

[JohnTitor]

Oh, sorry I thought this target had been already added but seems not.
We have to revert this to make CI green, could you re-submit this once the target is added on the rustc?