Move the dist-arm-linux job to arm runner

[MarcoIeni]

In rust CI, the dist-arm-linux job uses an x64 runner to cross-compile to arm.

Switch that job to use the large arm runner, similar to rust-lang/rust#133809 to improve performance.

[Kobzol]

The job is still being "cross-compiled" (using crosstool-ng), but it runs on an ARM runner now, thus saving CI cost. Implemented in rust-lang/rust#133902.

[MarcoIeni]

Should we remove crosstool-ng?

[Kobzol]

Well, if it works, it seems more elegant than doing the whole CentOS 7 dance where we compile the world from scratch. So in fact I would like to try the opposite (rust-lang/rust#134118) and replace CentOS with crosstool, if it is possible.

[MarcoIeni]

what about performance?
If we are already on arm, it seems a waste to cross compile to arm. Or am I missing something?

For the other runners, do you think it's worth to use arm to cross compile to x86 or there would be a performance penalty?

[Kobzol]

I haven't measured if the cross-compilation is slower or not, so hard to say 🤷‍♂ Same for the other question. I wouldn't overdo it though, just because the ARM runner are cheaper, it doesn't mean that we have to use them everywhere, crosscompilation in general is probably contains a can of worms, especially when it's actually being done across platforms.