New architecture support [LoongArch]

[yzewei]

[BackGround]
LoongArch is a new RISC ISA, which is independently designed by Loongson Technology.

LoongArch includes a reduced 32-bit version (LA32R), a standard 32-bit version (LA32S) and a 64-bit version (LA64), and loong64 is the 64-bit version of LoongArch.

LoongArch documentation: https://github.com/loongson/LoongArch-Documentation.git

[What do I want to do]
Provide the ci pipeline build part of loongarch

[yzewei]

@alex

[mayeut]

The same answers as #1426 apply here.
We'd need support from a base image. Ideally, RHEL (or a derivative like AlmaLinux/RockyLinux). However another base image might be okay for loongarch only.
Native CI availability is a must-have as qemu is a no go here as it is way to slow to build images (we were often hitting GHA time limit on ppc64le when travis-ci was broken on that architecture).

[yzewei]

Is it possible to use docker buildx?
Only qemu-user mode is applied

[mayeut]

This is what the ppc64le build was using on GHA. It's too slow.

[snnn]

Cross-compiling might be a possible solution. CPython's build system is autoconf/automake based, which supports cross-compiling very well. In theory we can get a LoongArch base image from somewhere, then cross-compiling all python versions for it, then copy the files into the image then publish the image. If just Python needs be handled in this way, it wouldn't be too hard. However, you may also need to build gcc/llvm from scratch, where you probably will also hit the time limit.
You cannot wait Github or Azure to have LoongArch available because cloud platforms only use very popular commodity available hardware. (This my personal opinion, doesn't represent the company).
On the other hand, Python is an open community. Nobody says you must use RHEL. You can build your wheels from any Linux distro then publish them to pypi as long as the tag you chose can be recognized by pip and auditwheel.