Auto merge of rust-lang#102732 - RalfJung:assert_unsafe_precondition2, r=bjorn3

nicer errors from assert_unsafe_precondition

This makes the errors shown by cargo-careful nicer, and since `panic_no_unwind` is `nounwind noreturn` it hopefully doesn't have bad codegen impact. Thanks to `@bjorn3` for the hint!

Would be nice if we could somehow supply our own (static) message to print, currently it always prints `panic in a function that cannot unwind`. But still, this is better than before.

Author: bors

tests/fail/function_calls/exported_symbol_bad_unwind2.rs

@@ -1,7 +1,7 @@
 //@revisions: extern_block definition both
 #![feature(rustc_attrs, c_unwind)]
 
-#[cfg_attr(any(definition, both), rustc_allocator_nounwind)]
+#[cfg_attr(any(definition, both), rustc_nounwind)]
 #[no_mangle]
 extern "C-unwind" fn nounwind() {
     //[definition]~^ ERROR: abnormal termination: the program aborted execution
@@ -11,7 +11,7 @@ extern "C-unwind" fn nounwind() {
 
 fn main() {
     extern "C-unwind" {
-        #[cfg_attr(any(extern_block, both), rustc_allocator_nounwind)]
+        #[cfg_attr(any(extern_block, both), rustc_nounwind)]
         fn nounwind();
     }
     unsafe { nounwind() }