test: add test for fixed internal compiler error

Updates #35157 (the bug there was fixed by CL200861)

Change-Id: I67069207b4cdc2ad4a475dd0bbc8555ecc5f534f
Reviewed-on: https://go-review.googlesource.com/c/go/+/203598
Run-TryBot: Giovanni Bajo <rasky@develer.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alberto Donizetti <alb.donizetti@gmail.com>

test/fixedbugs/issue35157.go

+// compile
+
+// Copyright 2019 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 p
+
+func f() {
+	var i int
+	var b *bool
+	var s0, s1, s2 string
+
+	if *b {
+		s2 = s2[:1]
+		i = 1
+	}
+	s1 = s1[i:-i+i] + s1[-i+i:i+2]
+	s1 = s0[i:-i]
+}