cmd/compile: use Widthptr instead of Types[Tptr].Width

Change-Id: I21e3abcfd1859f933f55fe875476dec07e43b038
Reviewed-on: https://go-review.googlesource.com/38466
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

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

@@ -1003,7 +1003,7 @@ func methodsym(nsym *Sym, t0 *Type, iface int) *Sym {
 	suffix = ""
 	if iface != 0 {
 		dowidth(t0)
-		if t0.Width < Types[Tptr].Width {
+		if t0.Width < int64(Widthptr) {
 			suffix = "·i"
 		}
 	}

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

@@ -363,7 +363,7 @@ func methods(t *Type) []*Sig {
 
 		if !sig.isym.Siggen() {
 			sig.isym.SetSiggen(true)
-			if !eqtype(this, it) || this.Width < Types[Tptr].Width {
+			if !eqtype(this, it) || this.Width < int64(Widthptr) {
 				compiling_wrappers = 1
 				genwrapper(it, f, sig.isym, 1)
 				compiling_wrappers = 0

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

@@ -1701,13 +1701,13 @@ func genwrapper(rcvr *Type, method *Field, newnam *Sym, iface int) {
 
 	t := nod(OTFUNC, nil, nil)
 	l := []*Node{this}
-	if iface != 0 && rcvr.Width < Types[Tptr].Width {
+	if iface != 0 && rcvr.Width < int64(Widthptr) {
 		// Building method for interface table and receiver
 		// is smaller than the single pointer-sized word
 		// that the interface call will pass in.
 		// Add a dummy padding argument after the
 		// receiver to make up the difference.
-		tpad := typArray(Types[TUINT8], Types[Tptr].Width-rcvr.Width)
+		tpad := typArray(Types[TUINT8], int64(Widthptr)-rcvr.Width)
 		pad := nod(ODCLFIELD, newname(lookup(".pad")), typenod(tpad))
 		l = append(l, pad)
 	}