Add std::is_constant_evaluated support.

test/config_info.cpp

@@ -1196,6 +1196,7 @@ void print_boost_macros()
    PRINT_MACRO(BOOST_NO_CXX20_HDR_SPAN);
    PRINT_MACRO(BOOST_NO_CXX20_HDR_STOP_TOKEN);
    PRINT_MACRO(BOOST_NO_CXX20_HDR_SYNCSTREAM);
+   PRINT_MACRO(BOOST_NO_CXX20_IS_CONSTANT_EVALUATED);
    PRINT_MACRO(BOOST_NO_CXX98_BINDERS);
    PRINT_MACRO(BOOST_NO_CXX98_FUNCTION_BASE);
    PRINT_MACRO(BOOST_NO_CXX98_RANDOM_SHUFFLE);
@@ -1263,6 +1264,7 @@ void print_boost_macros()
 
 
 
+
    // END GENERATED BLOCK
 
    PRINT_MACRO(BOOST_CXX_VERSION);