A64: Fix compilation with clang

src/a64/macro-assembler-a64.h

Index: src/a64/macro-assembler-a64.h
diff --git a/src/a64/macro-assembler-a64.h b/src/a64/macro-assembler-a64.h
index 93e9e80d043deee744e2273396a9923864bcdbd9..43a69b89e4005ef9daa4c1b72fedacd3094ae5e5 100644
--- a/src/a64/macro-assembler-a64.h
+++ b/src/a64/macro-assembler-a64.h
@@ -2166,7 +2166,12 @@ class MacroAssembler : public Assembler {
 class InstructionAccurateScope BASE_EMBEDDED {
  public:
   InstructionAccurateScope(MacroAssembler* masm, size_t count = 0)
-      : masm_(masm), size_(count * kInstructionSize) {
+      : masm_(masm)
+#ifdef DEBUG
+        ,
+        size_(count * kInstructionSize)
+#endif
+  {
     masm_->StartBlockConstPool();
 #ifdef DEBUG
     if (count != 0) {
@@ -2189,8 +2194,8 @@ class InstructionAccurateScope BASE_EMBEDDED {
 
  private:
   MacroAssembler* masm_;
-  size_t size_;
 #ifdef DEBUG
+  size_t size_;
   Label start_;
   bool previous_allow_macro_instructions_;
 #endif