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>

win32/win32_compat.c

@@ -21,7 +21,7 @@ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 THE SOFTWARE.
 */
 
-#ifndef WIN32
+#ifndef _WIN32
 
 static int dummy ATTRIBUTE((unused));
 

win32/win32_compat.h

@@ -25,7 +25,7 @@ THE SOFTWARE.
 #ifndef win32_COMPAT_H_
 #define win32_COMPAT_H_
 
-#ifdef WIN32
+#ifdef _WIN32
 #define NO_IPv6 1
 
 #include <winsock2.h>
@@ -90,5 +90,5 @@ struct iovec {
 
 #define inline
 
-#endif // WIN32
+#endif // _WIN32
 #endif // win32_COMPAT_H_