Support no-op personality(2) bits

[EtiennePerot]

Description

The personality(2) system call is a set of per-task bits that influence task behavior. Most modern Linux applications do not use it as far as I can tell (otherwise I'd expect this system call would have come up before), but PulseAudio does. As part of its core library, it prints a user-visible warning in its logs when it fails:

    if (personality(PER_LINUX) < 0)
        pa_log_warn("Uh, personality() failed: %s", pa_cstrerror(errno));

The PER_LINUX personality is the default personality on Linux, so this is effectively a no-op on Linux. Therefore it should be harmless to have it behave the same way on gVisor: let it be a no-op. (Currently, it fails with EINVAL.)

Is this feature related to a specific bug?

No

Do you have a specific solution in mind?

gVisor should allow no-op personality bits to be set on tasks, and preserve its current behavior (EINVAL) for other personality bits.