sweet/benchmarks/go-build: use new diagnostics framework

Change-Id: I77f8b37288ee6bb72a34a46aac4450e40559caaf
Cq-Include-Trybots: luci.golang.try:x_benchmarks-gotip-linux-amd64-longtest
Reviewed-on: https://go-review.googlesource.com/c/benchmarks/+/600068
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
2 files changed