add missing header needed for windows compile
add missing header needed for windows compile

nickerso/libcellml,hsorby/libcellml,hsorby/libcellml,hsorby/libcellml,nickerso/libcellml,cellml/libcellml,hsorby/libcellml,nickerso/libcellml,cellml/libcellml,cellml/libcellml,nickerso/libcellml,cellml/libcellml