mikros: Send main return value to proc_man on exit

library/std/src/sys/pal/mikros/start.rs

@@ -12,7 +12,7 @@ pub extern "C" fn _start() {
     let argv;
     unsafe {
         asm!("int 0x80", in("rax") 19, lateout("rax") argv, lateout("rcx") argc);
-        main(argc, argv);
-        asm!("int 0x80", in("rax") 1);
+        let code = main(argc, argv);
+        crate::sys::os::exit(code);
     };
 }