Fix example code.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@40493 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/WritingAnLLVMPass.html b/docs/WritingAnLLVMPass.html
index c967000..58bea1a 100644
--- a/docs/WritingAnLLVMPass.html
+++ b/docs/WritingAnLLVMPass.html
@@ -320,6 +320,7 @@
     }
   };
   
+  char Hello::ID = 0;
   RegisterPass&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>");
 }
 </pre></div>