buildfarm server suddenly not talking to old SSL stacks?

My buildfarm animals dromedary and prairiedog have been failing since
around 9AM EDT on Sunday.  The buildfarm script output isn't very
detailed:

getting branches of interest (https://buildfarm.postgresql.org/branches_of_inte\
rest.txt) at ./run_branches.pl line 129.

but trying it manually yields

$ curl https://buildfarm.postgresql.org/branches_of_interest.txt
curl: (35) error:1407742E:SSL routines:SSL23_GET_SERVER_HELLO:tlsv1 alert protocol version

The same thing works fine on newer machines though, as does fetching with
http: instead of https:.  Have we done something recently to create an
incompatibility with old SSL stacks?

            regards, tom lane