Fix issue 11267.

Compiler yields compile error within a function witch used in unevaluate
context of constexpr function because of CWG 1581 [2].

1. https://llvm.org/bugs/show_bug.cgi?id=23135
2. http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#1581

include/boost/fusion/container/list/cons.hpp

@@ -73,7 +73,7 @@ namespace boost { namespace fusion
             : car(rhs.car), cdr(rhs.cdr) {}
 
         template <typename Sequence>
-        BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
+        BOOST_FUSION_GPU_ENABLED
         cons(
             Sequence const& seq
           , typename boost::enable_if<