[glib] gwin32networkmonitor: fix build with MSVC

[Tim-Philipp Müller <tpm src gnome org>]

commit 03d06c175ffb5f6942147de6fa972452d4ae97c3
Author: Tim-Philipp Müller <tim centricular com>
Date:   Tue Feb 20 00:56:35 2018 +0000

    gwin32networkmonitor: fix build with MSVC
    
    Don't include unistd.h unconditionally.

 gio/gwin32networkmonitor.c | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/gio/gwin32networkmonitor.c b/gio/gwin32networkmonitor.c
index 8380f0100..9a090af7a 100644
--- a/gio/gwin32networkmonitor.c
+++ b/gio/gwin32networkmonitor.c
@@ -21,7 +21,10 @@
 #include "config.h"
 
 #include <errno.h>
+
+#ifdef HAVE_UNISTD_H
 #include <unistd.h>
+#endif
 
 #include <winsock2.h>
 #include <ws2tcpip.h>