cmd/bent: log toolchain prior to compilation

Compilation may emit compilation benchmark results, so we need to log
the toolchain in use first.

For golang/go#57770.

Change-Id: Ia1fdbbabba9a556ff6be720fcd7455de23d3d147
Reviewed-on: https://go-review.googlesource.com/c/benchmarks/+/462956
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Auto-Submit: Michael Pratt <mpratt@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Michael Pratt <mpratt@google.com>
1 file changed