cmd/link: failure with SIGPIPE on freebsd-amd64-12_2 builder

[bcmills]

From a freebsd-amd64-12_2 TryBot for CL 361095 (https://storage.googleapis.com/go-build-log/ca2a905d/freebsd-amd64-12_2_3e16b82d.log):

go tool link: signal: broken pipe
go tool dist: Failed: exit status 1


Error: tests failed: dist test failed: go_test:net/http/httptrace: exit status 1

There are no other signs of errors on the TryBot; I'm not sure what would have caused this failure mode.