cmd/compile: fix CTNIL static data comments

Change-Id: I434f881c10dec41a802641db8873abf1353beba2
Reviewed-on: https://go-review.googlesource.com/20671
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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

@@ -328,7 +328,6 @@ func gdata(nam *Node, nr *Node, wid int) {
 			}
 
 		default:
-			// CTNILs don't reach gdata; search for CTNIL in sinit.go. Probably they should, eventually.
 			Fatalf("gdata unhandled OLITERAL %v", nr)
 		}
 

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

@@ -514,6 +514,7 @@ func staticname(t *Type, ctxt int) *Node {
 }
 
 func isliteral(n *Node) bool {
+	// Treat nils as zeros rather than literals.
 	if n.Op == OLITERAL {
 		if n.Val().Ctype() != CTNIL {
 			return true