The compiler now also prints column information - make sure we use
the correct regexp for compiler error cleanups. Accept both, error
positions with columns and without, since column printing may be
disabled with -gcflags=-C.

Fixes #20628.

Change-Id: I46dc921dd5c29d7b8172cd19a3df57951f60d889
Reviewed-on: https://go-review.googlesource.com/45612
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>