Replace WIN32 with _WIN32

Using WIN32 depends on the build environment defining the variable.
_WIN32 is a predefined MSVC macro and is always available.

Signed-off-by: Tim Crawford <crawfxrd@gmail.com>

lib/connect.c

@@ -15,7 +15,7 @@
    You should have received a copy of the GNU Lesser General Public License
    along with this program; if not, see <http://www.gnu.org/licenses/>.
 */
-#if defined(WIN32)
+#if defined(_WIN32)
 #include "win32/win32_compat.h"
 #else
 #include <unistd.h>