sweet/harnesses: log which go-build package fails to build
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 <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Run-TryBot: Michael Pratt <e7f1edc6d5aa9f6c8c377425db8f1a5816cbbb88@google.com>
Auto-Submit: Michael Pratt <e7f1edc6d5aa9f6c8c377425db8f1a5816cbbb88@google.com>
Reviewed-by: Bryan Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>

golang/benchmarks,golang/benchmarks