test: add regression test for issue 43942

CL 356011 fixed this issue too.

Fixes #43942

Change-Id: I35ad397e78eeb80eff3a4217c4d40f15d40bdebb
Reviewed-on: https://go-review.googlesource.com/c/go/+/423814
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

test/fixedbugs/issue43942.go

@@ -0,0 +1,48 @@
+// run
+
+// Copyright 2022 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
+
+import "log"
+
+func main() {
+	defer func() {
+		expect(5, recover())
+	}()
+	func() {
+		expect(nil, recover())
+		defer func() {
+			defer func() {
+				defer func() {
+					defer func() {
+						expect(3, recover())
+					}()
+					defer panic(3)
+					panic(2)
+				}()
+				defer func() {
+					expect(1, recover())
+				}()
+				panic(1)
+			}()
+		}()
+	}()
+	func() {
+		for {
+			defer func() {
+				defer panic(5)
+			}()
+			break
+		}
+		panic(4)
+	}()
+}
+
+func expect(want, have interface{}) {
+	if want != have {
+		log.Fatalf("want %v, have %v", want, have)
+	}
+}