feat: support other library's hooking sigill, other misc Alaska fixes

[difcsi]

No description provided.

[stephenrkell]

Would it be feasible to separate out the "other" Alaska fixes from the issue of chained SIGILL handlers? It may be better to review them separately.

On the topic of keeping around a list of trap sites, I have a plan for this already, but it would not work quite the same way as your code. Since I want to allow use of an offline pass to identify trap sites (also addressing the startup performance issues), the list could be acquired from outside (e.g. from a file) or, as a fallback, computed on demand by walking the instructions as at present.