cmd/compile: add automated rewrite cycle detection

A common bug during development is to introduce rewrite rule cycles.
This is annoying because it takes a while to notice that
make.bash is a bit too slow this time, and to remember why.
And then you have to manually arrange to debug.

Make this all easier by automating it.
Detect cycles, and when we detect one, print the sequence
of rewrite rules that occur within a single cycle before crashing.

Change-Id: I8dadda13990ab925a81940d4833c9e5243368435
Reviewed-on: https://go-review.googlesource.com/c/go/+/347829


Trust: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>