[builtins] fix load of surrogate pair for BE platform

src/builtins/builtins-string.cc

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/builtins/builtins.h"
 #include "src/builtins/builtins-utils.h"
 
 #include "src/code-factory.h"
 #include "src/regexp/regexp-utils.h"
 
@@ skipping 1362 matching lines @@
         assembler->Uint32LessThan(lead, assembler->Int32Constant(0xDC00)));
     assembler->Assert(assembler->Uint32GreaterThanOrEqual(
         trail, assembler->Int32Constant(0xDC00)));
     assembler->Assert(
         assembler->Uint32LessThan(trail, assembler->Int32Constant(0xE000)));
 #endif
 
     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: {
         // Convert UTF16 surrogate pair into |word32| code point, encoded as
         // UTF32.
         Node* surrogate_offset =
             assembler->Int32Constant(0x10000 - (0xD800 << 10) - 0xDC00);
 
         // (lead << 10) + trail + SURROGATE_OFFSET
         var_result.Bind(assembler->Int32Add(
@@ skipping 92 matching lines @@
         Runtime::kThrowIncompatibleMethodReceiver, context,
         assembler->HeapConstant(assembler->factory()->NewStringFromAsciiChecked(
             "String Iterator.prototype.next", TENURED)),
         iterator);
     assembler->Return(result);  // Never reached.
   }
 }
 
 }  // namespace internal
 }  // namespace v8