cmd/internal/gc: make Node.Readonly a bool

Convert Node.Readonly to a bool.

Change-Id: Ide9f6f657f498d70d7b9544a38046325d7c82dc8
Reviewed-on: https://go-review.googlesource.com/6809Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/internal/gc/gsubr.go

@@ -208,7 +208,7 @@ func ggloblnod(nam *Node) {
 	p.To.Sym = nil
 	p.To.Type = obj.TYPE_CONST
 	p.To.Offset = nam.Type.Width
-	if nam.Readonly != 0 {
+	if nam.Readonly {
 		p.From3.Offset = obj.RODATA
 	}
 	if nam.Type != nil && !haspointers(nam.Type) {

src/cmd/internal/gc/sinit.go

@@ -521,7 +521,7 @@ func staticname(t *Type, ctxt int) *Node {
 	statuniqgen++
 	n := newname(Lookup(namebuf))
 	if ctxt == 0 {
-		n.Readonly = 1
+		n.Readonly = true
 	}
 	addvar(n, t, PEXTERN)
 	return n

src/cmd/internal/gc/syntax.go

@@ -45,7 +45,7 @@ type Node struct {
 	Initorder      uint8
 	Used           uint8
 	Isddd          uint8
-	Readonly       uint8
+	Readonly       bool
 	Implicit       uint8
 	Addrtaken      uint8 // address taken, even if not moved to heap
 	Assigned       uint8 // is the variable ever assigned to