Skip autoloading when there are errors.

This fix should be generalized such that upon autoloading we should be able to
check whether cling issued an error and abort the whole autoloading.

core/meta/src/TClingCallbacks.cxx

@@ -294,7 +294,15 @@ bool TClingCallbacks::tryAutoloadInternal(llvm::StringRef Name, LookupResult &R,
            // 'neutral' token, this will force clang to create the so called in
            // C++11 EmptyDecl. It is not a big issue, but still suboptimal.
            cling::Transaction* T = 0;
-           m_Interpreter->declare("namespace " + Name.str() + "{}", &T);
+           // For now rely on a side effect in cling. When there was an error
+           // all subsequent transaction coming from the autoloading will be 
+           // unsuccessful, because cling is on the error path, before trying
+           // to recover.
+           // FIXME: In future that might change so heads up.
+           cling::Interpreter::CompilationResult CR
+              = m_Interpreter->declare("namespace " + Name.str() + "{}", &T);
+           if (CR == cling::Interpreter::kFailure)
+              return false;
            pushedDCAndS.pop();
            cleanupRAII.pop();
            // The first decl in T will be EmptyDecl unless the FIXME above gets