Reorder body of begin_panic for consistency.

In the other functions, we put the struct and impl blocks first,
such that the return expression can be at the end of the body as usual.

std/src/panicking.rs

@@ -687,26 +687,10 @@ pub const fn begin_panic<M: Any + Send>(msg: M) -> ! {
         intrinsics::abort()
     }
 
-    let loc = Location::caller();
-    return crate::sys_common::backtrace::__rust_end_short_backtrace(move || {
-        rust_panic_with_hook(
-            &mut Payload::new(msg),
-            loc,
-            /* can_unwind */ true,
-            /* force_no_backtrace */ false,
-        )
-    });
-
     struct Payload<A> {
         inner: Option<A>,
     }
 
-    impl<A: Send + 'static> Payload<A> {
-        fn new(inner: A) -> Payload<A> {
-            Payload { inner: Some(inner) }
-        }
-    }
-
     unsafe impl<A: Send + 'static> PanicPayload for Payload<A> {
         fn take_box(&mut self) -> *mut (dyn Any + Send) {
             // Note that this should be the only allocation performed in this code path. Currently
@@ -729,14 +713,24 @@ pub const fn begin_panic<M: Any + Send>(msg: M) -> ! {
         }
     }
 
-    impl<A: Send + 'static> fmt::Display for Payload<A> {
+    impl<A: 'static> fmt::Display for Payload<A> {
         fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
             match &self.inner {
                 Some(a) => f.write_str(payload_as_str(a)),
                 None => process::abort(),
             }
         }
     }
+
+    let loc = Location::caller();
+    crate::sys_common::backtrace::__rust_end_short_backtrace(move || {
+        rust_panic_with_hook(
+            &mut Payload { inner: Some(msg) },
+            loc,
+            /* can_unwind */ true,
+            /* force_no_backtrace */ false,
+        )
+    })
 }
 
 fn payload_as_str(payload: &dyn Any) -> &str {