[glibmm] Variant: Avoid unused declaration warnings.

[Murray Cumming <murrayc src gnome org>]

commit d699cfb7213966f62941c882e54e39895ce489d6
Author: Murray Cumming <murrayc murrayc com>
Date:   Fri May 26 15:01:20 2017 +0200

    Variant: Avoid unused declaration warnings.

 glib/src/variant.hg |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/glib/src/variant.hg b/glib/src/variant.hg
index be7452b..1ca472d 100644
--- a/glib/src/variant.hg
+++ b/glib/src/variant.hg
@@ -1310,7 +1310,7 @@ const VariantType& Variant<std::tuple<Types...>>::variant_type()
 
   // expands the variadic template parameters
   using swallow = int[]; // ensures left to right order
-  swallow{(expander(Variant<Types>::variant_type()))...};
+  (void)swallow{(expander(Variant<Types>::variant_type()))...};
   static auto type = VariantType::create_tuple(types);
 
   return type;
@@ -1402,7 +1402,7 @@ std::tuple<Types...> Variant<std::tuple<Types...>>::get() const
     variants.push_back(variant);
     return i++;
   };
-  swallow{(expander(get_child_variant<Types>(i)))...};
+  (void)swallow{(expander(get_child_variant<Types>(i)))...};
   detail::assign_tuple(variants, data, std::index_sequence_for<Types...>{});
 
   return data;