*: check defined(_WIN32) instead of defined(WIN32)

Only _WIN32 is defined by the compiler, and WIN32 is not standardized
and may be missing.

Closes #169

src/event/MultiSocketMonitor.cxx

@@ -23,7 +23,7 @@
 
 #include <algorithm>
 
-#ifndef WIN32
+#ifndef _WIN32
 #include <poll.h>
 #endif
 
@@ -50,7 +50,7 @@ MultiSocketMonitor::ClearSocketList()
 	fds.clear();
 }
 
-#ifndef WIN32
+#ifndef _WIN32
 
 void
 MultiSocketMonitor::ReplaceSocketList(pollfd *pfds, unsigned n)

src/event/MultiSocketMonitor.hxx

@@ -31,7 +31,7 @@
 
 #include <assert.h>
 
-#ifdef WIN32
+#ifdef _WIN32
 /* ERROR is a WIN32 macro that poisons our namespace; this is a kludge
    to allow us to use it anyway */
 #ifdef ERROR
@@ -39,7 +39,7 @@
 #endif
 #endif
 
-#ifndef WIN32
+#ifndef _WIN32
 struct pollfd;
 #endif
 
@@ -189,7 +189,7 @@ public:
 		}
 	}
 
-#ifndef WIN32
+#ifndef _WIN32
 	/**
 	 * Replace the socket list with the given file descriptors.
 	 * The given pollfd array will be modified by this method.

src/event/ServerSocket.cxx

@@ -43,7 +43,7 @@
 #include <unistd.h>
 #include <assert.h>
 
-#ifdef WIN32
+#ifdef _WIN32
 #include <ws2tcpip.h>
 #include <winsock.h>
 #else

src/event/SignalMonitor.cxx

@@ -20,7 +20,7 @@
 #include "config.h"
 #include "SignalMonitor.hxx"
 
-#ifndef WIN32
+#ifndef _WIN32
 
 #include "SocketMonitor.hxx"
 #include "util/Manual.hxx"

src/event/SignalMonitor.hxx

@@ -24,7 +24,7 @@
 
 class EventLoop;
 
-#ifndef WIN32
+#ifndef _WIN32
 
 #include "util/BindMethod.hxx"
 

src/event/SocketMonitor.cxx

@@ -24,7 +24,7 @@
 
 #include <assert.h>
 
-#ifdef WIN32
+#ifdef _WIN32
 #include <winsock2.h>
 #else
 #include <sys/socket.h>

src/event/SocketMonitor.hxx

@@ -28,7 +28,7 @@
 #include <assert.h>
 #include <stddef.h>
 
-#ifdef WIN32
+#ifdef _WIN32
 /* ERROR is a WIN32 macro that poisons our namespace; this is a kludge
    to allow us to use it anyway */
 #ifdef ERROR