Apply `-Zpanic-abort-tests` to doctests too
### What does this PR try to resolve?
`cranelift` doesn't support unwinding, which causes issues with `should_panic` tests. Attempting to use `-Zpanic-abort-tests` to fix that still fails with doctests because they attempt to use unwinding. `rustdoc` already supports specifying `-Cpanic=abort` and correctly handles ` ```should_panic` tests with it enabled, so we can just start passing it when `-Zpanic-abort-tests` is set.
Fixes https://github.com/rust-lang/rust/issues/120578 (when using `-Zbuild-std=std,panic_abort` too)