Analyser: make sure that we can mark a constant as an external variable.
Analyser: make sure that we can mark a constant as an external variable.

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