[giac] force Giac for Windows installer/portable

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@25705 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
4.9.136.0

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@25706 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e