go/types: less closure creations in gcimporter.

Closures are incredibly expensive on linux/arm due to
repetitive flush of instruction cache.

go test -short on ODROID-X:

Before:
ok      exp/gotype      17.091s
ok      go/types        2.225s

After:
ok      exp/gotype      7.193s
ok      go/types        1.143s

R=dave, minux.ma, rsc
CC=golang-dev, remy
https://golang.org/cl/7062045

src/pkg/go/types/gcimporter.go

@@ -408,18 +408,13 @@ func (p *gcParser) parseField() *Field {
 func (p *gcParser) parseStructType() Type {
 	var fields []*Field
 
-	parseField := func() {
-		fields = append(fields, p.parseField())
-	}
-
 	p.expectKeyword("struct")
 	p.expect('{')
-	if p.tok != '}' {
-		parseField()
-		for p.tok == ';' {
-			p.next()
-			parseField()
+	for p.tok != '}' {
+		if len(fields) > 0 {
+			p.expect(';')
 		}
+		fields = append(fields, p.parseField())
 	}
 	p.expect('}')
 
@@ -450,7 +445,11 @@ func (p *gcParser) parseParameter() (par *Var, isVariadic bool) {
 // ParameterList = { Parameter "," } Parameter .
 //
 func (p *gcParser) parseParameters() (list []*Var, isVariadic bool) {
-	parseParameter := func() {
+	p.expect('(')
+	for p.tok != ')' {
+		if len(list) > 0 {
+			p.expect(',')
+		}
 		par, variadic := p.parseParameter()
 		list = append(list, par)
 		if variadic {
@@ -460,15 +459,6 @@ func (p *gcParser) parseParameters() (list []*Var, isVariadic bool) {
 			isVariadic = true
 		}
 	}
-
-	p.expect('(')
-	if p.tok != ')' {
-		parseParameter()
-		for p.tok == ',' {
-			p.next()
-			parseParameter()
-		}
-	}
 	p.expect(')')
 
 	return
@@ -509,20 +499,15 @@ func (p *gcParser) parseSignature() *Signature {
 func (p *gcParser) parseInterfaceType() Type {
 	var methods []*Method
 
-	parseMethod := func() {
-		name := p.parseName()
-		typ := p.parseSignature()
-		methods = append(methods, &Method{name, typ})
-	}
-
 	p.expectKeyword("interface")
 	p.expect('{')
-	if p.tok != '}' {
-		parseMethod()
-		for p.tok == ';' {
-			p.next()
-			parseMethod()
+	for p.tok != '}' {
+		if len(methods) > 0 {
+			p.expect(';')
 		}
+		name := p.parseName()
+		typ := p.parseSignature()
+		methods = append(methods, &Method{name, typ})
 	}
 	p.expect('}')