ghc-heap: fix HalfWord incompatible Binary instances for cross GHC

ghc-heap defines HalfWord as Word32/Word16 depending on host word
size. For cross GHC with different host/target word sizes, the Binary
instances are incompatible and breaks iserv serialization of any
message type that involves HalfWord, breaking the ghci debugger. This
patch fixes the issue and has been tested to fix ghci debugger
functionality of the wasm backend. Fixes #25420 #25781.

(cherry picked from commit b228fcb5)

libraries/ghc-heap/GHC/Exts/Heap/InfoTable/Types.hsc

 {-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE DerivingStrategies #-}
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+
 module GHC.Exts.Heap.InfoTable.Types
     ( StgInfoTable(..)
     , EntryFunPtr
-    , HalfWord
+    , HalfWord(..)
     , ItblCodes
     ) where
 
@@ -18,13 +21,16 @@ type ItblCodes = Either [Word8] [Word32]
 #include "ghcautoconf.h"
 -- Ultra-minimalist version specially for constructors
 #if SIZEOF_VOID_P == 8
-type HalfWord = Word32
+type HalfWord' = Word32
 #elif SIZEOF_VOID_P == 4
-type HalfWord = Word16
+type HalfWord' = Word16
 #else
 #error Unknown SIZEOF_VOID_P
 #endif
 
+newtype HalfWord = HalfWord HalfWord'
+    deriving newtype (Enum, Eq, Integral, Num, Ord, Real, Show, Storable)
+
 type EntryFunPtr = FunPtr (Ptr () -> IO (Ptr ()))
 
 -- | This is a somewhat faithful representation of an info table. See

libraries/ghci/GHCi/Message.hs

@@ -498,6 +498,10 @@ instance Binary (FunPtr a) where
   put = put . castFunPtrToPtr
   get = castPtrToFunPtr <$> get
 
+instance Binary Heap.HalfWord where
+  put x = put (fromIntegral x :: Word32)
+  get = fromIntegral <$> (get :: Get Word32)
+
 -- Binary instances to support the GetClosure message
 #if MIN_VERSION_ghc_heap(8,11,0)
 instance Binary Heap.StgTSOProfInfo