Rollup merge of #26761 - steveklabnik:actually_ub, r=alexcrichton

I incorrectly stated that it's an abort.

r? @Gankro

src/doc/trpl/ffi.md

@@ -533,19 +533,10 @@ attribute turns off Rust's name mangling, so that it is easier to link to.
 
 # FFI and panics
 
-It’s important to be mindful of `panic!`s when working with FFI. This code,
-when called from C, will `abort`:
-
-```rust
-#[no_mangle]
-pub extern fn oh_no() -> ! {
-    panic!("Oops!");
-}
-# fn main() {}
-```
-
-If you’re writing code that may panic, you should run it in another thread,
-so that the panic doesn’t bubble up to C:
+It’s important to be mindful of `panic!`s when working with FFI. A `panic!`
+across an FFI boundary is undefined behavior. If you’re writing code that may
+panic, you should run it in another thread, so that the panic doesn’t bubble up
+to C:
 
 ```rust
 use std::thread;