Introduce intrinsic to expose debug state to generated code.

src/debug.h

Index: src/debug.h
diff --git a/src/debug.h b/src/debug.h
index 7f9b1a2eb0297eaf502b85d4cb2ccb47759a6ae4..b672940c0f9ef58738c3d2dfeb8bfc91267b9526 100644
--- a/src/debug.h
+++ b/src/debug.h
@@ -505,6 +505,10 @@ class Debug {
   int break_id() { return thread_local_.break_id_; }
 
   // Support for embedding into generated code.
+  Address is_active_address() {
+    return reinterpret_cast<Address>(&is_active_);
+  }
+
   Address after_break_target_address() {
     return reinterpret_cast<Address>(&after_break_target_);
   }