440ac656 forgot to also guard the
chmod and thus 64bit builds on windows fail when attempting to sign, as
in this case there is no cross-compiled explorer extension and the dlls
are not copied into instdir

Change-Id: Ie17a079b64256d3ef0bf253bdda6cfe722dac3e2
Reviewed-on: https://gerrit.libreoffice.org/44076Reviewed-by: Christian Lohmaier <lohmaier+LibreOffice@googlemail.com>
Tested-by: Christian Lohmaier <lohmaier+LibreOffice@googlemail.com>