`panic_immediate_abort` doesn't work on nightly 2025-09-24 or newer

[samestep]

The Remove panic String Formatting with panic_immediate_abort section works fine with Rust nightly 2025-09-23 or earlier, but starting with Rust nightly 2025-09-24, it fails with this error message:

error: panic_immediate_abort is now a real panic strategy! Enable it with the compiler flags `-Zunstable-options -Cpanic=immediate-abort`
  --> /nix/store/rvp07m5kwy20sl6wdabkyg6skqammhdh-rust-default-1.92.0-nightly-2025-09-24/lib/rustlib/src/rust/library/core/src/panicking.rs:36:1
   |
36 | / compile_error!(
37 | |     "panic_immediate_abort is now a real panic strategy! \
38 | |     Enable it with the compiler flags `-Zunstable-options -Cpanic=immediate-abort`"
39 | | );
   | |_^

I'm not quite sure what the right fix is; I tried passing those -Zunstable-options -Cpanic=immediate-abort flags as directed by the new error message, but that just gives me a different error:

error: unexpected argument '-C' found

Usage: cargo build [OPTIONS]

For more information, try '--help'.

[johnthagen]

Might be worth asking a question on https://internals.rust-lang.org/?

[samestep]

Never mind, I figured it out! See #86.