internal/bisect: add 'q' hash option for quiet hash behavior switching

internal/bisect: add 'q' hash option for quiet hash behavior switching

This is intended for the specific case of 'fmahash=qn' where someone
wants to disable fma without all the hash-search-handshake output.
There are cases where arm64, ppc64, and s390x users might want to do
this.

Change-Id: Iaf46c68a00d7c9f7f82fd98a4548b72610f84bed
Reviewed-on: https://go-review.googlesource.com/c/go/+/503776
Run-TryBot: David Chase <drchase@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>