Switch almost all of Pal to Rusty error handling.

src/header/stdlib/mod.rs

@@ -1320,7 +1320,7 @@ pub unsafe extern "C" fn system(command: *const c_char) -> c_int {
         unreachable!();
     } else if child_pid > 0 {
         let mut wstatus = 0;
-        if Sys::waitpid(child_pid, &mut wstatus, 0) == !0 {
+        if Sys::waitpid(child_pid, &mut wstatus, 0).or_minus_one_errno() == -1 {
             return -1;
         }