Add symex-backtrace

[smowton]

Here's a useful function, mainly for calling from the debugger or temporary debug prints, that gives a backtrace of symex's current callstack.

[tautschnig]

I agree that this could be useful, but it badly needs comments: neither the commit message nor the implementation provide any. As is, @romainbrenguier surely would remove it upon the next cleanup!

[smowton]

@tautschnig added

[allredj]

🚫
This PR failed Diffblue compatibility checks (cbmc commit: b34875a).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/92714166
Status will be re-evaluated on next push.
Please contact @peterschrammel, @thk123, or @allredj for support.

Common spurious failures:

• the cbmc commit has disappeared in the mean time (e.g. in a force-push)
• the author is not in the list of contributors (e.g. first-time contributors).

The incompatibility may have been introduced by an earlier PR. In that case merging this
PR should be avoided unless it fixes the current incompatibility.

[romainbrenguier]

⛏️ I would suggest the slighly nicer:

for(const auto &frame : make_range(
    threads[source.thread_nr].call_stack.rbegin(),
    threads[source.thread_nr].call_stack.rend()))

[romainbrenguier]

@tautschnig

I agree that this could be useful, but it badly needs comments: neither the commit message nor the implementation provide any. As is, @romainbrenguier surely would remove it upon the next cleanup!

👍

[smowton]

@romainbrenguier those comments have been added. Nice as ranges are, I think I'll restrict using them to when I want their mapping / filtering action, rather than just to permit c++11 syntax ;)