runtime: fix output for bad pcHeader

runtime: fix output for bad pcHeader

With print, the output all runs together.
Take this opportunity to clean up and label all the fields.
Print pluginpath unilaterally; no reason not to.
Wrap long lines. Remove pointless newline from throw.

Change-Id: I37af15dc8fcb3dbdbc6da8bbea2c0ceaf7b5b889
Reviewed-on: https://go-review.googlesource.com/c/go/+/350734
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>