test/fixedbugs: forgotten test cases for issues 3907 and 4156.

Update #3907.
Update #4156.

R=golang-dev, dave
CC=golang-dev
https://golang.org/cl/6595044

test/fixedbugs/bug455.go

+// run
+
+// 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 4156: out of fixed registers when chaining method calls.
+// Used to happen with 6g.
+
+package main
+
+type test_i interface {
+	Test() test_i
+	Result() bool
+}
+
+type test_t struct {
+}
+
+func newTest() *test_t {
+	return &test_t{}
+}
+
+type testFn func(string) testFn
+
+func main() {
+	test := newTest()
+
+	switch {
+	case test.
+		Test().
+		Test().
+		Test().
+		Test().
+		Test().
+		Test().
+		Test().
+		Test().
+		Test().
+		Test().
+		Result():
+		// case worked
+	default:
+		panic("Result returned false unexpectedly")
+	}
+}
+
+func (t *test_t) Test() test_i {
+	return t
+}
+
+func (t *test_t) Result() bool {
+	return true
+}

test/fixedbugs/bug456.go

+// run
+
+// 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 3907: out of fixed registers in nested byte multiply.
+// Used to happen with both 6g and 8g.
+
+package main
+
+func F(a, b, c, d uint8) uint8 {
+	return a * (b * (c * (d *
+		(a * (b * (c * (d *
+			(a * (b * (c * (d *
+				a * (b * (c * d)))))))))))))
+}
+
+func main() {
+	var a, b, c, d uint8 = 1, 1, 1, 1
+	x := F(a, b, c, d)
+	if x != 1 {
+		println(x)
+		panic("x != 1")
+	}
+}