Add select() to std for darwin.

[il-k]

select() is left out from zig's std. Yet, it still has an important role in darwin systems: darwin does not support poll(), nor kqueue() for polling tty files. It appears the only way to do it, sadly, is to use select().

It would be nice if it was made available in standard library for darwin.

[ifreund]

My first thought was "Please no, select is always a footgun because of the fd limit" but from the article linked it seems macOS has a workaround for that:

The avid reader might be wondering: “what if we have more than 1024 file descriptors? select is not going to work!” You’re right! This was a problem, so let’s enter The OSX select(2) Trick II: _DARWIN_UNLIMITED_SELECT.

This little gem hidden in the manual page tells us that if _DARWIN_UNLIMITED_SELECT is defined at compilation time, we are allowed to go beyond the FD_SETSIZE limit! We cannot create the fd_set as usual nor use FD_ZERO, we’ll need to manually allocate it and zero it with memset: 1, 2, 3.

I think that it would be reasonable to force usage of this darwin workaround for select if adding it to the standard library.

I don't think select should be added for any target for which it is not required, it's too big of a footgun on most unix like systems.