external-stg-interpreter: support new decodeDouble_Int64#

This change fixes this compilation error:

  lib/Stg/Interpreter/PrimOp/Double.hs:126:22: error: [GHC-83865]
      • Couldn't match expected type ‘Int#’ with actual type ‘Int64#’
      • In the first argument of ‘I#’, namely ‘a’
        In the first argument of ‘Int64V’, namely ‘(I# a)’
        In the expression: Int64V (I# a)
      |
  126 |     pure [Int64V (I# a), IntV (I# b)]

Author: TristanCacqueray

external-stg-interpreter/lib/Stg/Interpreter/PrimOp/Double.hs

@@ -1,4 +1,4 @@
-{-# LANGUAGE RecordWildCards, LambdaCase, OverloadedStrings, PatternSynonyms, MagicHash, UnboxedTuples, BangPatterns, Strict #-}
+{-# LANGUAGE RecordWildCards, LambdaCase, OverloadedStrings, PatternSynonyms, MagicHash, UnboxedTuples, BangPatterns, Strict, CPP #-}
 module Stg.Interpreter.PrimOp.Double where
 
 import GHC.Word
@@ -123,6 +123,11 @@ evalPrimOp fallback op args t tc = case (op, args) of
   ( "decodeDouble_Int64#", [DoubleV (D# x)]) -> do
     -- NOTE: map back to GHC primop
     let !(# a, b #) = decodeDouble_Int64# x
-    pure [Int64V (I# a), IntV (I# b)]
+#if MIN_VERSION_base(4,18,0)
+    let a' = int64ToInt# a
+#else
+    let a' = a
+#endif
+    pure [Int64V (I# a'), IntV (I# b)]
 
   _ -> fallback op args t tc