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.
Makes our error coverage a little more consistent across the board by
applying it to Linux side of things as well. This also makes it more
consistent with the warning settings in other libraries in the project.
This also updates httplib to 0.7.9, as there are several warning
cleanups made that allow us to enable several warnings as errors.
