Figure out pstack and Rust strip = "symbols" interaction

(writing up a quick summary so I don't forget about this)

@jclulow reported to me that a hung nextest process didn't show its symbols in pstack. It turned out that was because the build process we were using within nextest was stripping all symbols.

I tried switching to strip = "debuginfo" but that didn't seem to help. The only thing that caused stacks to show up in pstack was strip = "none".

In https://github.com/nextest-rs/nextest/commit/d4f982b3184f07ff5c40cc90c52d3fc6567be0b9#commitcomment-140289873, Taiki believes that this is a bug (there was apparently a similar bug in MSVC as well.) I tried setting up a small project to investigate:

https://github.com/sunshowers/pstack-test

but found that even with the strip-symbols profile (which activates strip = "symbols"), pstack could show function symbols. Not quite clear why that would be happening though!

Start with the issue's observations about Rust's strip settings and the linked pstack-test project, then review the referenced nextest commit discussion. Reproduce the difference between strip = "symbols", strip = "debuginfo", and strip = "none" with pstack; done means the interaction and cause are explained clearly.