Actually, two enum classes, since for some reason there are two separate
yet identical `PollFD` types used in the codebase. I get that one is
ABI-compatible with the Switch while the other is an abstract type used
for the host, but why not use `WSAPOLLFD` directly for the latter?
Anyway, why make this change? Because on Apple platforms, `POLL_IN`,
`POLL_OUT`, etc. (with an underscore) are defined as macros in
<sys/signal.h>. (This is inherited from FreeBSD.) So defining
a variable with the same name causes a compile error.
I could just rename the variables, but while I was at it I thought I
might as well switch to an enum for stronger typing.
Also, change the type used for values copied directly to/from the
`events` and `revents` fields of the host *native*
`pollfd`/`WSASPOLLFD`, from `u32` to `short`, as `short` is the correct
canonical type on both Unix and Windows.
This commit adds a network abstraction designed to implement bsd:s but
at the same time work as a generic abstraction to implement any
networking code we have to use from core.
This is implemented on top of BSD sockets on Unix systems and winsock on
Windows. The code is designed around winsocks having compatibility
definitions to support both BSD and Windows sockets.
