Unwinding into FFI is undefined behavior

[janderholm]

Some of the examples are using the assert! macro. This will panic and thus unwind. Unwinding across FFI boundaries however is undefined behavior and needs to be catched.

This can be solved either by:

1. Build with panic = "abort" in cargo.toml
2. Use std::panic::catch_unwind to catch the unwinding before it hits FFI code
3. Same as 2. but made easier by using the macro callback_guard! from the glib crate

I prefer number 1 (better performance) as long as the library created does not actively use unwinding, for example by restarting paniced threads. Since unwinding is a very important topic when it comes to FFI I think there should be a chapter with pros and cons in the book.

[jhg]

Maybe it changed: rust-lang/rust#58760

The default was changed to abort-by-default in extern functions in this PR.

rust-lang/rust#55982