cmd/compile: allow unnamed constants to set line number

Fixes #8836.

Change-Id: Idda9f4a987e03b3bdf5e8fdb984fe56d6f84aa59
Reviewed-on: https://go-review.googlesource.com/11672
Reviewed-by: David Chase <drchase@google.com>

src/cmd/compile/internal/gc/subr.go

@@ -231,9 +231,15 @@ func setlineno(n *Node) int32 {
 	lno := lineno
 	if n != nil {
 		switch n.Op {
-		case ONAME, OTYPE, OPACK, OLITERAL:
+		case ONAME, OTYPE, OPACK:
 			break
 
+		case OLITERAL:
+			if n.Sym != nil {
+				break
+			}
+			fallthrough
+
 		default:
 			lineno = n.Lineno
 			if lineno == 0 {

test/fixedbugs/issue8836.go

@@ -0,0 +1,24 @@
+// errorcheck
+
+// Copyright 2015 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Checking that line number is correct in error message.
+
+package main
+
+type Cint int
+
+func foobar(*Cint, Cint, Cint, *Cint)
+
+func main() {
+	a := Cint(1)
+
+	foobar(
+		&a,
+		0,
+		0,
+		42, // ERROR ".*"
+	)
+}