Only disable placement-new warning under gcc >= 6
Otherwise this would create unknown option warnings under g++ < 6.
diff --git a/include/pybind11/pybind11.h b/include/pybind11/pybind11.h
index b7833fc..3c9e691 100644
--- a/include/pybind11/pybind11.h
+++ b/include/pybind11/pybind11.h
@@ -82,12 +82,12 @@
/* Store the capture object directly in the function record if there is enough space */
if (sizeof(capture) <= sizeof(rec->data)) {
-#if defined(__GNUG__) && !defined(__clang__)
+#if defined(__GNUG__) && !defined(__clang__) && __GNUC__ >= 6
# pragma GCC diagnostic push
# pragma GCC diagnostic ignored "-Wplacement-new"
#endif
new ((capture *) &rec->data) capture { std::forward<Func>(f) };
-#if defined(__GNUG__) && !defined(__clang__)
+#if defined(__GNUG__) && !defined(__clang__) && __GNUC__ >= 6
# pragma GCC diagnostic pop
#endif
if (!std::is_trivially_destructible<Func>::value)