Support LinkRuntimeCallback() with RS compiler.

Change-Id: I28ada4e7c462cb9673de6886d934dce855fac339
diff --git a/cpu_ref/rsCpuScript.h b/cpu_ref/rsCpuScript.h
index 2197a20..53835bd 100644
--- a/cpu_ref/rsCpuScript.h
+++ b/cpu_ref/rsCpuScript.h
@@ -78,6 +78,7 @@
 
     virtual Allocation * getAllocationForPointer(const void *ptr) const;
 
+    virtual  void * getRSExecutable() { return mExecutable; }
 
 protected:
     RsdCpuReferenceImpl *mCtx;