gio tool: Fix build on Windows/non-GCC

The recently-added GIO tools is intended to be built on all platforms, so
adjust the code a bit to enable this:

-Use gssize instead of ssize_t, as ssize_t is not supported by all
 compilers.
-Include io.h on Windows, and define STDIN_FILENO and STDOUT_FILENO if
 necessary on Windows.

https://bugzilla.gnome.org/show_bug.cgi?id=768357

gio/gio-tool-cat.c

@@ -23,6 +23,18 @@
 #include <gi18n.h>
 #include <errno.h>
 
+#ifdef G_OS_WIN32
+#include <io.h>
+#endif
+
+#ifndef STDOUT_FILENO
+#define STDOUT_FILENO 1
+#endif
+
+#ifdef HAVE_UNISTD_H
+#include <unistd.h>
+#endif
+
 #include "gio-tool.h"
 
 
@@ -56,7 +68,7 @@ cat (GFile *file)
       res = 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/gio-tool-save.c

@@ -22,8 +22,19 @@
 #include <gio/gio.h>
 #include <gi18n.h>
 
-#include "gio-tool.h"
+#ifdef G_OS_WIN32
+#include <io.h>
+#endif
 
+#ifndef STDIN_FILENO
+#define STDIN_FILENO 0
+#endif
+
+#ifdef HAVE_UNISTD_H
+#include <unistd.h>
+#endif
+
+#include "gio-tool.h"
 
 static char *etag = NULL;
 static gboolean backup = FALSE;
@@ -84,7 +95,7 @@ save (GFile *file)
       res = read (STDIN_FILENO, buffer, 1024);
       if (res > 0)
 	{
-	  ssize_t written;
+	  gssize written;
 
 	  p = buffer;
 	  while (res > 0)