Fix build with statvfs

As pointed out in bug 704587, the maze of ifdefs was missing the
variable declaration for statfs_result in one case.

https://bugzilla.gnome.org/show_bug.cgi?id=704587

gio/glocalfile.c

@@ -2440,6 +2440,7 @@ is_remote_fs (const gchar *filename)
 
 #elif defined(USE_STATVFS)
   struct statvfs statfs_buffer;
+  int statfs_result = 0;
 
   statfs_result = statvfs (filename, &statfs_buffer);
 #else