cmd/compile: fix position of fake receivers; be more careful in logopt

The src.NoXPos in fake receivers was leaking, through a series of
mishaps, all the way to logopt.  If done just so, this can lead to
a compiler crash.  This makes logopt crash-proof and eliminates the
root cause as well.

I'm reluctant to write a test for this because it's kinda slow
and involved; my working test is "compile something that mentions
the flag package with -json=0,$TMPDIR flag, then be sure that
$TMPDIR/flag/__unnamed__.json was not created".

Change-Id: I384b717c0e7522953d22d61f7e06319e11192d7d
Reviewed-on: https://go-review.googlesource.com/c/go/+/443156
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>

0 files changed, 0 insertions, 0 deletions