Use vDSO on Linux 6.11

[ericlagergren]

See golang/go#69577

[briansmith]

I think this would be good to have opt-in for a while, while the DSO feature is being tested in the real world.

[newpavlov]

This may be interesting in the context of #424, but otherwise I think we should just use libc::getrandom (maybe through dlopen in the backend with /dev/urandom fallback) and let it decide how the syscall is handled.

[newpavlov]

Closing in favor of #508 and bytecodealliance/rustix#1185.