...when instantiating implicitly defined special member functions of
XMLSECURITY_DLLPUBLIC XMLSignatureHelper, due to mpXSecController member

Change-Id: Ifd504c1b215a8a1a86d7a9d660aa569b75e07d50
Reviewed-on: https://gerrit.libreoffice.org/73406
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>