Intrinsify UserTag operations on all architectures

runtime/vm/isolate.h

Index: runtime/vm/isolate.h
diff --git a/runtime/vm/isolate.h b/runtime/vm/isolate.h
index 8dcb630173d212f0d15698f100b8838a7d0f6eeb..88c8744f64bd034973ed95f3d333892d77e46e83 100644
--- a/runtime/vm/isolate.h
+++ b/runtime/vm/isolate.h
@@ -477,6 +477,12 @@ class Isolate : public BaseIsolate {
   uword user_tag() const {
     return user_tag_;
   }
+  static intptr_t user_tag_offset() {
+    return OFFSET_OF(Isolate, user_tag_);
+  }
+  static intptr_t current_tag_offset() {
+    return OFFSET_OF(Isolate, current_tag_);
+  }
 
   RawGrowableObjectArray* tag_table() const { return tag_table_; }
   void set_tag_table(const GrowableObjectArray& value);