std: add seteuid/setegid to std.os
std: add seteuid/setegid to std.os

Currently these are only implemented for linux.

raulgrell/zig,raulgrell/zig,raulgrell/zig,zig-lang/zig,andrewrk/zig,zig-lang/zig,zig-lang/zig,raulgrell/zig,raulgrell/zig,andrewrk/zig