Rollup merge of #81530 - ojeda:sys-use-abort-instead-of-wasm32-unreachable, r=Mark...

Rollup merge of #81530 - ojeda:sys-use-abort-instead-of-wasm32-unreachable, r=Mark-Simulacrum

sys: use `process::abort()` instead of `arch::wasm32::unreachable()`

Rationale:

  - `abort()` lowers to `wasm32::unreachable()` anyway.
  - `abort()` isn't `unsafe`.
  - `abort()` matches the comment better.
  - `abort()` avoids confusion by future readers (e.g. https://github.com/rust-lang/rust/pull/81527): the naming of wasm's `unreachable` instruction is a bit unfortunate because it is not related to the `unreachable()` intrinsic (intended to trigger UB).

Codegen is likely to be different since `unreachable()` is `inline` while `abort()` is `cold`. Since it doesn't look like we are expecting here to trigger this case, the latter seems better anyway.