Implement an ability to only run tests on a particular platform

[nagisa]

Currently we have an ability to specify targets to ignore tests on some platforms in form of //ignore-<arch> comment appearing somewhere in the file.

These attributes, however, are hardly usable when a test is intended to target a single architecture, as you’d have to specify every architecture test is not targeting.

The idea is to implement an attribute // only-<target>, which essentially an equivalent to specifying // ignore-* for every target but the <target>.

The relevant location to change would be here.

[Pulkit07]

Thanks for the file link. I am going to try fix this.

[ollie27]

dupe of #33581?

[Pulkit07]

@ollie27 yes looks like so. I will jump to that. Thanks.

[nagisa]

Well, this has (admittedly terse) instructions. Just make sure to note both issues as "Fixed" when submitting a PR, that’s about it.