gio/tests: Clean up inclusion of unistd.h

Include unistd.h only on *NIX and define items as necessary on Windows,
also replace instances of ssize_t with the GLib-equivilant gssize so to fix
the build on platforms that do not have ssize_t, such as Visual C++.

https://bugzilla.gnome.org/show_bug.cgi?id=711047

gio/tests/filter-cat.c

@@ -23,13 +23,22 @@
 #include <config.h>
 
 #include <stdio.h>
-#include <unistd.h>
 #include <locale.h>
 #include <errno.h>
 
 #include <glib.h>
 #include <gio/gio.h>
 
+#ifdef G_OS_UNIX
+#include <unistd.h>
+#endif
+
+#ifdef G_OS_WIN32
+#ifndef STDOUT_FILENO
+#define STDOUT_FILENO 1
+#endif
+#endif
+
 static gchar **locations = NULL;
 static char *from_charset = NULL;
 static char *to_charset = NULL;
@@ -157,7 +166,7 @@ cat (GFile * file)
 	g_input_stream_read (in, buffer, sizeof (buffer) - 1, NULL, &error);
       if (res > 0)
 	{
-	  ssize_t written;
+	  gssize written;
 
 	  p = buffer;
 	  while (res > 0)

gio/tests/gsubprocess-testprog.c

@@ -3,8 +3,8 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <errno.h>
-#include <unistd.h>
 #ifdef G_OS_UNIX
+#include <unistd.h>
 #include <gio/gunixinputstream.h>
 #include <gio/gunixoutputstream.h>
 #endif
@@ -20,7 +20,7 @@ write_all (int           fd,
 {
   while (len > 0)
     {
-      ssize_t bytes_written = write (fd, buf, len);
+      gssize bytes_written = write (fd, buf, len);
       if (bytes_written < 0)
 	g_error ("Failed to write to fd %d: %s",
 		 fd, strerror (errno));

gio/tests/readwrite.c

@@ -1,9 +1,12 @@
 #include <glib/glib.h>
 #include <glib/gstdio.h>
 #include <gio/gio.h>
-#include <unistd.h>
 #include <string.h>
 
+#ifdef G_OS_UNIX
+#include <unistd.h>
+#endif
+
 static const char *original_data = "This is some test data that we can put in a file...";
 static const char *new_data = "new data..";
 

gio/tests/resolver.c

@@ -28,7 +28,9 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#ifdef G_OS_UNIX
 #include <unistd.h>
+#endif
 
 #include <gio/gio.h>
 

gio/tests/win32-streams.c

@@ -27,7 +27,6 @@
 #include <string.h>
 #include <fcntl.h>
 #include <io.h>
-#include <unistd.h>
 
 #include <windows.h>