Added OpenBSD support to wasmtime's signals.rs

[CalebHeydon]

This pull request adds support for OpenBSD to the wasmtime-runtime crate. The change is very small. It just adds a case for OpenBSD on x86_64. I'm not trying to port the entire project to OpenBSD. I'm just trying to get this crate to work because I am trying to get the Zed editor to run on OpenBSD.

[alexcrichton]

Thanks!

[fitzgen]

Is there not an official openbsd target in rustup? I was looking at adding a CI check to ensure that this will keep compiling in the future, and I didn't see anything. I find that a little surprising.

[cfallin]

Unfortunately no, because OpenBSD is explicit about not guaranteeing kernel ABI stability between releases (sort of the opposite of the Linux kernel's never-break-userland rule).

In my limited explorations here, on a native OpenBSD system the package system does have Rust but it's quickly out of date; the only way to have a current Rust compiler is to run OpenBSD -CURRENT (the development branch) with its version of the package tree.

(To @CalebHeydon: at one point I got all of wasmtime building and working on OpenBSD in #2980, but abandoned the effort because keeping everything up-to-date and building given the above vs. MSRV policies was just too much work. Maybe things will change eventually!)

[lcheylus]

@CalebHeydon Thanks for your fix to add support for OpenBSD. With it, I was able to build successfully Yara-X https://github.com/VirusTotal/yara-x :)