More constexpr and noexcept support.

Note 1: Forwarding functions are specified as a C++14 constexpr since
std::forward is not a constexpr within C++11.

Note 2: Though I'm not sure why it doesn't compile, some declarations
are specified as a C++14 constexpr or non-constexpr.

Note 3: Boost.Tuple adaptation and TR1-based tuple implementations are
not constexpr.

include/boost/fusion/container/map/convert.hpp

@@ -17,7 +17,7 @@ namespace boost { namespace fusion { namespace detail
     {
         typedef typename result_of::value_of<It>::type type;
 
-        BOOST_FUSION_GPU_ENABLED
+        BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
         static inline type call(It const& it)
         {
             return *it;
@@ -31,7 +31,7 @@ namespace boost { namespace fusion { namespace detail
         typedef typename result_of::value_of_data<It>::type data_type;
         typedef typename fusion::pair<key_type, data_type> type;
 
-        BOOST_FUSION_GPU_ENABLED
+        BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
         static inline type call(It const& it)
         {
             return type(deref_data(it));
@@ -69,7 +69,7 @@ namespace boost { namespace fusion
     }
 
     template <typename Sequence>
-    BOOST_FUSION_GPU_ENABLED
+    BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
     inline typename result_of::as_map<Sequence>::type
     as_map(Sequence& seq)
     {
@@ -78,7 +78,7 @@ namespace boost { namespace fusion
     }
 
     template <typename Sequence>
-    BOOST_FUSION_GPU_ENABLED
+    BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
     inline typename result_of::as_map<Sequence const>::type
     as_map(Sequence const& seq)
     {
@@ -101,7 +101,7 @@ namespace boost { namespace fusion
                     result_of::as_map<Sequence>::type
                 type;
 
-                BOOST_FUSION_GPU_ENABLED
+                BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
                 static type call(Sequence& seq)
                 {
                     typedef result_of::as_map<Sequence> gen;