proposal: x/sys/unix: add SetMempolicy

[kolyshkin]

Proposal Details

Since Linux v2.6.7 there is a set_mempolicy(2) system call, described here.

It would be nice to have a wrapper for it and definitions for related constants and data types.

Implementation can look like this: https://go-review.googlesource.com/c/sys/+/704535

[gopherbot]

Change https://go.dev/cl/704535 mentions this issue: unix: add SetMemPolicy and its mode/flag values

[ianlancetaylor]

We don't normally require a proposal just to add a new system call and new constants to the x/sys/unix package. We only require a proposal if there is something out of the ordinary about this system call; in this case I don't see anything. The system call should be defined by a ``//sysor//sysnb` comment in syscall_linux.go; it should not be a hand-written function that calls `RawSyscall`.

[kolyshkin]

Closing as per previous comment