work around variadicity mismatch when marking functions private
work around variadicity mismatch when marking functions private

The real issue is frontends constructing a mismatch in Call type at the
Call site and the called entity. However as these are hard to fix and
the fix here shouldn't hurt we do it in firm for now.

jonashaag/libfirm,MatzeB/libfirm,8l/libfirm,8l/libfirm,8l/libfirm,8l/libfirm,libfirm/libfirm,davidgiven/libfirm,jonashaag/libfirm,davidgiven/libfirm,jonashaag/libfirm,MatzeB/libfirm,jonashaag/libfirm,jonashaag/libfirm,killbug2004/libfirm,killbug2004/libfirm,jonashaag/libfirm,MatzeB/libfirm,davidgiven/libfirm,davidgiven/libfirm,8l/libfirm,MatzeB/libfirm,libfirm/libfirm,MatzeB/libfirm,MatzeB/libfirm,libfirm/libfirm,8l/libfirm,killbug2004/libfirm,8l/libfirm,killbug2004/libfirm,libfirm/libfirm,killbug2004/libfirm,libfirm/libfirm,MatzeB/libfirm,davidgiven/libfirm,killbug2004/libfirm,killbug2004/libfirm,davidgiven/libfirm,jonashaag/libfirm,davidgiven/libfirm