cmd/compile/internal/gc: eliminate two uses of Type.Pos

Instead we can use t.nod.Pos.

Change-Id: I643ee3226e402e38d4c77e8f328cbe83e55eac5c
Reviewed-on: https://go-review.googlesource.com/38309
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

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

@@ -126,7 +126,7 @@ func dowidth(t *Type) {
 	if t.Width == -2 {
 		if !t.Broke() {
 			t.SetBroke(true)
-			yyerrorl(t.Pos, "invalid recursive type %v", t)
+			yyerrorl(t.nod.Pos, "invalid recursive type %v", t)
 		}
 
 		t.Width = 0
@@ -143,7 +143,10 @@ func dowidth(t *Type) {
 	defercalc++
 
 	lno := lineno
-	lineno = t.Pos
+	if t.nod != nil {
+		lineno = t.nod.Pos
+	}
+
 	t.Width = -2
 	t.Align = 0
 

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

@@ -3822,6 +3822,7 @@ func typecheckdef(n *Node) *Node {
 		}
 		n.Walkdef = 1
 		n.Type = typ(TFORW)
+		n.Type.nod = n
 		n.Type.Sym = n.Sym // TODO(gri) this also happens in typecheckdeftype(n) - where should it happen?
 		nerrors0 := nerrors
 		typecheckdeftype(n)