Thank you for the link. With this ticket, the gurobi and cplex backends still fail because I don't have gurobi and cplex installed. It would be nice if that was detected earlier in the process and the build failed right away. Actually, it is detected early in the process:
/bin/sh: gurobi.sh: No such file or directory
GUROBI_HOME is not set, or it does not point to a directory with a Gurobi installation. Trying to link against -lgurobi
but the installation proceeds anyway. But this is a separate issue.