build fix

apparently harfbuzz is not build with std=c++11 everywhere

Change-Id: Ie105706212d9dd32f33bc67c8a878ce8a55e60ef
Reviewed-on: https://gerrit.libreoffice.org/32521Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Jochen Nitschke <j.nitschke+logerrit@ok.de>

external/harfbuzz/ubsan.patch

@@ -58,7 +58,7 @@
    template <typename T>
    inline const Type *bsearch (T *key) const
    {
-+    if (len == 0) return nullptr;
++    if (len == 0) return NULL;
      return (const Type *) ::bsearch (key, array, len, sizeof (Type), (hb_compare_func_t) Type::cmp);
    }