include/compat: Add missing win32 type and constant definitions

include/compat: Add missing win32 type and constant definitions

The following types and constants are not defined on Windows, for
which reason we're going to include them in compat.h.

* uid_t, gid_t
* sigset_t
* HOST_NAME_MAX
* O_CLOEXEC, which we're going to define as a no-op. By default,
  handles are not inherited by subprocesses.
* SHUT_* flags
* loff_t
* __STRING
* EBADE, ENODATA, ESHUTDOWN, ESTALE, EREMOTEIO
* suseconds_t
* SIGKILL, SIGINT - we're mostly going to stub signal handling
on Windows

Also, we'll have to make sure that pipe_cloexec uses C style linking,
which would otherwise be affected as the include order changes.

timeval.tv_sec is defined as long instead of time_t on Windows[1], which
we'll have to take into account.

[1] https://docs.microsoft.com/en-us/windows/win32/api/winsock/ns-winsock-timeval

Signed-off-by: Lucian Petrut <lpetrut@cloudbasesolutions.com>