x/sys/unix: expose padding fields on s390x or hide them on other architectures #18632
Description
When the s390x port was upstreamed it was decided that 'to try and stop the bleeding' we would avoid exposing 'internal' fields (usually prefixed with X__) in structs in the syscall package, instead replacing them with blank identifiers. This work then also made its way into x/sys/unix.
Unfortunately every now and again it turns out that someone is using a field we blanked out, for example: #18628 and #17298. This is annoying because while the code in question is probably doing something unpleasant it makes the process of enabling a package on s390x harder than it needs to be.
I would like to propose that we either expose these fields on s390x (only where they exist on other architectures already of course) OR we use blank identifiers for them on other architectures too. Exposing them on s390x is easy, but maybe removing them from the API is more desirable in the long run.