[glibmm] ustring: #include <cstddef> unconditionally

[Daniel Boles <dboles src gnome org>]

commit cbfbe10d20230c01960c48f4e9decf467f01f9b8
Author: Daniel Boles <dboles src gnome org>
Date:   Thu Jul 6 21:55:24 2017 +0100

    ustring: #include <cstddef> unconditionally
    
    It may not be needed for std::ptrdiff_t, as that is only used
    conditionally, but we use std::size_t either way in some Stringify
    specialisations, and while that is almost certain to be pulled in from
    <string> or some other standard header, we might as well be explicit.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=784211

 glib/glibmm/ustring.h |    4 +---
 1 files changed, 1 insertions(+), 3 deletions(-)
---
diff --git a/glib/glibmm/ustring.h b/glib/glibmm/ustring.h
index 7489126..7a07848 100644
--- a/glib/glibmm/ustring.h
+++ b/glib/glibmm/ustring.h
@@ -21,13 +21,11 @@
 #include <glibmm/unicode.h>
 #include <glib.h>
 
+#include <cstddef> // for std::size_t and optionally std::ptrdiff_t
 #include <iosfwd>
 #include <iterator>
 #include <sstream>
 #include <string>
-#ifndef GLIBMM_HAVE_STD_ITERATOR_TRAITS
-#include <cstddef> /* for std::ptrdiff_t */
-#endif
 
 namespace Glib
 {