Add BOOST_INLINE_CONSTEXPR convenience macro

include/boost/config/detail/suffix.hpp

@@ -1003,6 +1003,8 @@ namespace std{ using ::type_info; }
 #define BOOST_INLINE_VARIABLE
 #endif
 
+#define BOOST_INLINE_CONSTEXPR  BOOST_INLINE_VARIABLE BOOST_CONSTEXPR_OR_CONST
+
 //
 // Unused variable/typedef workarounds:
 //