test: add test for unused calls to builtin functions

R=gri
CC=golang-dev
https://golang.org/cl/6871054

test/fixedbugs/issue4463.go

+// errorcheck
+
+// Copyright 2012 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.
+
+// Issue 4463: test builtin functions in statement context and in
+// go/defer functions.
+
+package p
+
+import "unsafe"
+
+func F() {
+	var a []int
+	var c chan int
+	var m map[int]int
+	var s struct{ f int }
+
+	append(a, 0)			// ERROR "not used"
+	cap(a)				// ERROR "not used"
+	complex(1, 2)			// ERROR "not used"
+	imag(1i)			// ERROR "not used"
+	len(a)				// ERROR "not used"
+	make([]int, 10)			// ERROR "not used"
+	new(int)			// ERROR "not used"
+	real(1i)			// ERROR "not used"
+	unsafe.Alignof(a)		// ERROR "not used"
+	unsafe.Offsetof(s.f)		// ERROR "not used"
+	unsafe.Sizeof(a)		// ERROR "not used"
+
+	close(c)
+	copy(a, a)
+	delete(m, 0)
+	panic(0)
+	print("foo")
+	println("bar")
+	recover()
+
+	(close(c))
+	(copy(a, a))
+	(delete(m, 0))
+	(panic(0))
+	(print("foo"))
+	(println("bar"))
+	(recover())
+
+	go append(a, 0)			// ERROR "not used"
+	go cap(a)			// ERROR "not used"
+	go complex(1, 2)		// ERROR "not used"
+	go imag(1i)			// ERROR "not used"
+	go len(a)			// ERROR "not used"
+	go make([]int, 10)		// ERROR "not used"
+	go new(int)			// ERROR "not used"
+	go real(1i)			// ERROR "not used"
+	go unsafe.Alignof(a)		// ERROR "not used"
+	go unsafe.Offsetof(s.f)		// ERROR "not used"
+	go unsafe.Sizeof(a)		// ERROR "not used"
+
+	go close(c)
+	go copy(a, a)
+	go delete(m, 0)
+	go panic(0)
+	go print("foo")
+	go println("bar")
+	go recover()
+
+	defer append(a, 0)		// ERROR "not used"
+	defer cap(a)			// ERROR "not used"
+	defer complex(1, 2)		// ERROR "not used"
+	defer imag(1i)			// ERROR "not used"
+	defer len(a)			// ERROR "not used"
+	defer make([]int, 10)		// ERROR "not used"
+	defer new(int)			// ERROR "not used"
+	defer real(1i)			// ERROR "not used"
+	defer unsafe.Alignof(a)		// ERROR "not used"
+	defer unsafe.Offsetof(s.f)	// ERROR "not used"
+	defer unsafe.Sizeof(a)		// ERROR "not used"
+
+	defer close(c)
+	defer copy(a, a)
+	defer delete(m, 0)
+	defer panic(0)
+	defer print("foo")
+	defer println("bar")
+	defer recover()
+}