fix Framework Codesigning on MacOSX

on the 32 bits build 10.6 SDK we deliver Python Framework
The code to sign the framework, although clearly the command that
is recommanded for such things, failed with
"object file format invalid"

This patch make it 'works'... and with it the 10.6 build does not
complain anymore about not satsifying it's 'requierments'

Change-Id: I4fb5c6f3a9ed573d0bb2a09bddaf44300dc6f98b
Reviewed-on: https://gerrit.libreoffice.org/7152
Reviewed-by: Christian Lohmaier <lohmaier+LibreOffice@googlemail.com>
Tested-by: Christian Lohmaier <lohmaier+LibreOffice@googlemail.com>