Make Win64 compile.

src/mark-compact.h

Index: src/mark-compact.h
diff --git a/src/mark-compact.h b/src/mark-compact.h
index 4b94b3111b93d667ec7f48cdbee780b494813a3c..75ec76ccfcd8fd483a4ce4f4eca212ae8b3b5325 100644
--- a/src/mark-compact.h
+++ b/src/mark-compact.h
@@ -188,7 +188,7 @@ class MarkingDeque {
     HeapObject** obj_low = reinterpret_cast<HeapObject**>(low);
     HeapObject** obj_high = reinterpret_cast<HeapObject**>(high);
     array_ = obj_low;
-    mask_ = RoundDownToPowerOf2(obj_high - obj_low) - 1;
+    mask_ = RoundDownToPowerOf2(static_cast<int>(obj_high - obj_low)) - 1;
     top_ = bottom_ = 0;
     overflowed_ = false;
   }
@@ -248,10 +248,10 @@ class MarkingDeque {
   }
 
   HeapObject** array() { return array_; }
-  intptr_t bottom() { return bottom_; }
-  intptr_t top() { return top_; }
-  intptr_t mask() { return mask_; }
-  void set_top(intptr_t top) { top_ = top; }
+  int bottom() { return bottom_; }
+  int top() { return top_; }
+  int mask() { return mask_; }
+  void set_top(int top) { top_ = top; }
 
  private:
   HeapObject** array_;