Complaints about compile errors in a-except.adb

When I attempt to build a project (that built OK in ObjectAda) with GPS 2.1
I see a series of errors in file a-except.a:

1417:17 invalid operator types for operator "<"
...(etc)

I reinstalled GNAT 3.15p to see if this would help, but no joy.

Am I missing switches that will make this go away?

Thanks,
Brian  bgbell (at) acm.org