cmd/compile: sort interface methods in tointerface0

Might as well sort them while they're still in a slice.

Change-Id: I40c25ddc5c054dcb4da2aeefa79947967609d599
Reviewed-on: https://go-review.googlesource.com/20591
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

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

@@ -7,6 +7,7 @@ package gc
 import (
 	"cmd/internal/obj"
 	"fmt"
+	"sort"
 	"strings"
 )
 
@@ -975,6 +976,7 @@ func tointerface0(t *Type, l []*Node) *Type {
 			fields = append(fields, f)
 		}
 	}
+	sort.Sort(methcmp(fields))
 	t.SetFields(fields)
 
 	for f, it := IterFields(t); f != nil && !t.Broke; f = it.Next() {
@@ -984,7 +986,6 @@ func tointerface0(t *Type, l []*Node) *Type {
 	}
 
 	checkdupfields("method", t)
-	t = sortinter(t)
 	checkwidth(t)
 
 	return t

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

@@ -416,13 +416,6 @@ func (x methcmp) Less(i, j int) bool {
 	return false
 }
 
-func sortinter(t *Type) *Type {
-	s := t.FieldSlice()
-	sort.Sort(methcmp(s))
-	t.SetFields(s)
-	return t
-}
-
 func Nodintconst(v int64) *Node {
 	c := Nod(OLITERAL, nil, nil)
 	c.Addable = true