Update no_std_swap test

Add `#![crate_type="lib"]` annotation to test and remove `panic_handler`

Author: dswij

tests/ui/crate_level_checks/no_std_swap.rs

@@ -1,5 +1,6 @@
 #![no_std]
 #![feature(lang_items, start, libc)]
+#![crate_type = "lib"]
 
 use core::panic::PanicInfo;
 
@@ -12,12 +13,3 @@ fn main() {
     a = b;
     b = a;
 }
-
-#[allow(clippy::empty_loop)]
-#[panic_handler]
-fn panic(_info: &PanicInfo) -> ! {
-    loop {}
-}
-
-#[lang = "eh_personality"]
-extern "C" fn eh_personality() {}

tests/ui/crate_level_checks/no_std_swap.stderr

@@ -1,5 +1,5 @@
 error: this looks like you are trying to swap `a` and `b`
-  --> $DIR/no_std_swap.rs:12:5
+  --> $DIR/no_std_swap.rs:13:5
    |
 LL | /     a = b;
 LL | |     b = a;