XSecController must be a complete type here (Windows --disable-pch)

...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>

xmlsecurity/inc/xmlsignaturehelper.hxx

@@ -26,10 +26,10 @@
 #include <svl/sigstruct.hxx>
 #include "xmlsecuritydllapi.h"
 #include "xmlsignaturehelper.hxx"
+#include "xsecctl.hxx"
 
 class DateTime;
 class UriBindingHelper;
-class XSecController;
 
 namespace com {
 namespace sun {