test: match gccgo error messages

assign.go:59:28: error: ‘x’ repeated on left side of :=
assign.go:65:20: error: ‘a’ repeated on left side of :=

method2.go:36:11: error: reference to method ‘val’ in type that is pointer to interface, not interface
method2.go:37:11: error: reference to method ‘val’ in type that is pointer to interface, not interface

Change-Id: I8f385c75a82fae4eacf4618df8f9f65932826494
Reviewed-on: https://go-review.googlesource.com/c/go/+/274447


Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>