Fixes:

- Add missing virtual destructor on `SSLBackend`.

- On Windows, filter out `POLLWRBAND` (one of the new flags added) when
  calling `WSAPoll`, because despite the constant being defined on
  Windows, passing it calls `WSAPoll` to yield `EINVAL`.

- Reduce OpenSSL version requirement to satisfy CI; I haven't tested
  whether it actually builds (or runs) against 1.1.1, but if not, I'll
  figure it out.

- Change an instance of memcpy to memmove, even though the arguments
  cannot overlap, to avoid a [strange GCC
  error](https://github.com/yuzu-emu/yuzu/pull/10912#issuecomment-1606283351).