debug/gosym: add hook to disable recovers

debug/gosym: add hook to disable recovers

debug/gosym assumes throughout that bogus input means a malformed file.
That's generally true, but not when you're changing the package.
In that case, the panic usually indicates a newly introduced bug,
and seeing the panic is really useful.

Add a manually-enabled way to make panics panic.

Change-Id: I07af6c7b982c4cf61180db29f07aa63576ba7837
Reviewed-on: https://go-review.googlesource.com/c/go/+/352949
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>