Fix unittest build with GCC older than 5.

Old GCCs have an annoying bug where RVO disables the automatic
conversion to base for unique_ptr. Add a pessimizing std::move as a
workaround.

llvm-svn: 335854

clang/unittests/StaticAnalyzer/RegisterCustomCheckersTest.cpp

@@ -61,7 +61,7 @@ public:
     AnalysisConsumer->AddCheckerRegistrationFn([](CheckerRegistry &Registry) {
       Registry.addChecker<CustomChecker>("custom.CustomChecker", "Description");
     });
-    return AnalysisConsumer;
+    return std::move(AnalysisConsumer);
   }
 };