runtime: fix problem with repeated panic/recover/re-panics and open-coded defers

In the open-code defer implementation, we add defer struct entries to the defer
chain on-the-fly at panic time to represent stack frames that contain open-coded
defers. This allows us to process non-open-coded and open-coded defers in the
correct order. Also, we need somewhere to be able to store the 'started' state of
open-coded defers. However, if a recover succeeds, defers will now be processed
inline again (unless another panic happens). Any defer entry representing a frame
with open-coded defers will become stale once we run the corresponding defers
inline and exit the associated stack frame. So, we need to remove all entries for
open-coded defers at recover time.

The current code was only removing the top-most open-coded defer from the defer
chain during recovery. However, with recursive functions that do repeated
panic-recover-repanic, multiple stale entries can accumulate on the chain. So, we
just adjust the loop to process the entire chain. Since this is at panic/recover
case, it is fine to scan through the entire chain (which should usually have few
elements in it, since most defers are open-coded).

The added test fails with a SEGV without the fix, because it tries to run a stale
open-code defer entry (and the stack has changed).

Fixes #37664.

Change-Id: I8e3da5d610b5e607411451b66881dea887f7484d
Reviewed-on: https://go-review.googlesource.com/c/go/+/222420


Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>