Fix A64 build: unwrap HSourcePosition into int before recording.

src/a64/lithium-a64.h

Index: src/a64/lithium-a64.h
diff --git a/src/a64/lithium-a64.h b/src/a64/lithium-a64.h
index dddb0ad009e7ea50f171f40bda26faf093819aea..acfdb8fcfb803c045896c8543082f59c87d94fa3 100644
--- a/src/a64/lithium-a64.h
+++ b/src/a64/lithium-a64.h
@@ -2827,7 +2827,6 @@ class LChunkBuilder V8_FINAL : public LChunkBuilderBase {
         current_instruction_(NULL),
         current_block_(NULL),
         allocator_(allocator),
-        position_(RelocInfo::kNoPosition),
         instruction_pending_deoptimization_environment_(NULL),
         pending_deoptimization_ast_id_(BailoutId::None()) { }
 
@@ -2956,7 +2955,6 @@ class LChunkBuilder V8_FINAL : public LChunkBuilderBase {
   HInstruction* current_instruction_;
   HBasicBlock* current_block_;
   LAllocator* allocator_;
-  int position_;
   LInstruction* instruction_pending_deoptimization_environment_;
   BailoutId pending_deoptimization_ast_id_;