More evaluation order tests, for global variables and switch.

gccgo currently fails this test.

R=rsc
CC=golang-dev
https://golang.org/cl/179108

test/fixedbugs/bug236.go

+// $G $D/$F.go && $L $F.$A && ./$A.out
+
+// Copyright 2009 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+var gen = 'a'
+
+func f(n int) string {
+	s := string(gen) + string(n+'A'-1)
+	gen++
+	return s
+}
+
+func g(x, y string) string { return x + y }
+
+var v1 = f(1) + f(2)
+var v2 = g(f(3), f(4))
+var v3 = f(5) + f(6) + f(7) + f(8) + f(9)
+
+func main() {
+	gen = 'a'
+
+	if v1 != "aAbB" {
+		panic("BUG: bug236a")
+	}
+	if v2 != "cCdD" {
+		panic("BUG: bug236b")
+	}
+	if v3 != "eEfFgGhHiI" {
+		panic("BUG: bug236c")
+	}
+
+	switch "aAbB" {
+	case f(1) + f(2):
+	default:
+		panic("BUG: bug236d")
+	}
+
+	switch "cCdD" {
+	case g(f(3), f(4)):
+	default:
+		panic("BUG: bug236e")
+	}
+
+	switch "eEfFgGhHiI" {
+	case f(5) + f(6) + f(7) + f(8) + f(9):
+	default:
+		panic("BUG: bug236f")
+	}
+}