make mapnik_value_type_t C++11-friendly

include/mapnik/value_types.hpp

@@ -25,6 +25,7 @@
 
 // mapnik
 #include <mapnik/config.hpp>
+#include <mapnik/cxx11_support.hpp>
 #include <mapnik/pixel_types.hpp>
 
 
@@ -34,7 +35,6 @@
 #pragma GCC diagnostic pop
 
 // stl
-#include <type_traits>
 #include <iosfwd>
 #include <cstddef>
 
@@ -160,13 +160,13 @@ namespace detail {
 //  value_double    if T is a floating-point type
 //  T &&            otherwise
 
-template <typename T, typename dT = std::decay_t<T>>
+template <typename T, typename dT = decay_t<T>>
 using mapnik_value_type_t =
-    std::conditional_t<
+    conditional_t<
         std::is_same<dT, bool>::value, value_bool,
-        std::conditional_t<
+        conditional_t<
             std::is_integral<dT>::value, value_integer,
-            std::conditional_t<
+            conditional_t<
                 std::is_floating_point<dT>::value, value_double,
                 T && >>>;