sweet/harnesses: log which go-build package fails to build

For golang/go#53572.

Change-Id: I6a90f20d7032b3e2d3989ae7357d0340854b5f64
Reviewed-on: https://go-review.googlesource.com/c/benchmarks/+/414396
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Michael Pratt <mpratt@google.com>
Auto-Submit: Michael Pratt <mpratt@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
1 file changed