unix: avoid fuzzy provenance casts

Co-authored-by: Jonas Böttiger <[email protected]>

Author: workingjubilee

library/std/src/sys/pal/unix/stack_overflow.rs

@@ -97,7 +97,7 @@ mod imp {
     ) {
         let (start, end) = GUARD.get();
         // SAFETY: this pointer is provided by the system and will always point to a valid `siginfo_t`.
-        let addr = unsafe { (*info).si_addr() as usize };
+        let addr = unsafe { (*info).si_addr().addr() };
 
         // If the faulting address is within the guard page, then we print a
         // message saying so and abort.