cmd/bent: added updated version of goawk

Kept the old one, since there were interesting structural changes
to the code.

Change-Id: I4bdecd4b2dce556dacc4a88d52ef804b590e5238
Reviewed-on: https://go-review.googlesource.com/c/benchmarks/+/432358
Reviewed-by: Michael Pratt <mpratt@google.com>
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>