[builtins] fix load of surrogate pair for BE platform

src/builtins/builtins-string.cc

Index: src/builtins/builtins-string.cc
diff --git a/src/builtins/builtins-string.cc b/src/builtins/builtins-string.cc
index 6b14e2510b773ea5f5004334041e174b043e3846..49fc6c28070186b6d713fd22aab4b147aa0943ab 100644
--- a/src/builtins/builtins-string.cc
+++ b/src/builtins/builtins-string.cc
@@ -1380,7 +1380,12 @@ compiler::Node* LoadSurrogatePairInternal(CodeStubAssembler* assembler,
     switch (encoding) {
       case UnicodeEncoding::UTF16:
         var_result.Bind(assembler->WordOr(
+// Need to swap the order for big-endian platforms
+#if V8_TARGET_BIG_ENDIAN
+            assembler->WordShl(lead, assembler->Int32Constant(16)), trail));
+#else
             assembler->WordShl(trail, assembler->Int32Constant(16)), lead));
+#endif
         break;
 
       case UnicodeEncoding::UTF32: {