Reintroduce the ASTConsumer/ASTUnit fix from r110610, it has nothing to do with the breakage.

llvm-svn: 110840
diff --git a/clang/lib/Frontend/ASTUnit.cpp b/clang/lib/Frontend/ASTUnit.cpp
index fe4768d..bbe2ec5 100644
--- a/clang/lib/Frontend/ASTUnit.cpp
+++ b/clang/lib/Frontend/ASTUnit.cpp
@@ -320,6 +320,9 @@
       Unit.addTopLevelDecl(D);
     }
   }
+
+  // We're not interested in "interesting" decls.
+  void HandleInterestingDecl(DeclGroupRef) {}
 };
 
 class TopLevelDeclTrackerAction : public ASTFrontendAction {