Merge branch 'develop' into cxx_version

Updates to C++20.

Resolved Conflicts:
	checks/Jamfile.v2
	checks/std/cpp_aggregate_bases_17.cpp
	checks/std/cpp_aggregate_nsdmi_14.cpp
	checks/std/cpp_alias_templates_11.cpp
	checks/std/cpp_aligned_new_17.cpp
	checks/std/cpp_attributes_11.cpp
	checks/std/cpp_binary_literals_14.cpp
	checks/std/cpp_capture_star_this_17.cpp
	checks/std/cpp_char8_t_20.cpp
	checks/std/cpp_conditional_explicit_20.cpp
	checks/std/cpp_constexpr_11.cpp
	checks/std/cpp_constexpr_14.cpp
	checks/std/cpp_constexpr_17.cpp
	checks/std/cpp_decltype_11.cpp
	checks/std/cpp_decltype_auto_14.cpp
	checks/std/cpp_deduction_guides_17.cpp
	checks/std/cpp_delegating_constructors_11.cpp
	checks/std/cpp_enumerator_attributes_17.cpp
	checks/std/cpp_exceptions_03.cpp
	checks/std/cpp_explicit_conversion_11.cpp
	checks/std/cpp_fold_expressions_17.cpp
	checks/std/cpp_generic_lambdas_14.cpp
	checks/std/cpp_guaranteed_copy_elision_17.cpp
	checks/std/cpp_hex_float_17.cpp
	checks/std/cpp_if_constexpr_17.cpp
	checks/std/cpp_impl_destroying_delete_20.cpp
	checks/std/cpp_impl_three_way_comparison_20.cpp
	checks/std/cpp_inheriting_constructors_11.cpp
	checks/std/cpp_inheriting_constructors_17.cpp
	checks/std/cpp_init_captures_14.cpp
	checks/std/cpp_initializer_lists_11.cpp
	checks/std/cpp_inline_variables_17.cpp
	checks/std/cpp_lambdas_11.cpp
	checks/std/cpp_lib_addressof_constexpr_17.cpp
	checks/std/cpp_lib_allocator_traits_is_always_equal_17.cpp
	checks/std/cpp_lib_any_17.cpp
	checks/std/cpp_lib_apply_17.cpp
	checks/std/cpp_lib_array_constexpr_17.cpp
	checks/std/cpp_lib_as_const_17.cpp
	checks/std/cpp_lib_atomic_is_always_lock_free_17.cpp
	checks/std/cpp_lib_atomic_ref_20.cpp
	checks/std/cpp_lib_bind_front_20.cpp
	checks/std/cpp_lib_bit_cast_20.cpp
	checks/std/cpp_lib_bool_constant_17.cpp
	checks/std/cpp_lib_boyer_moore_searcher_17.cpp
	checks/std/cpp_lib_byte_17.cpp
	checks/std/cpp_lib_char8_t_20.cpp
	checks/std/cpp_lib_chrono_17.cpp
	checks/std/cpp_lib_chrono_udls_14.cpp
	checks/std/cpp_lib_clamp_17.cpp
	checks/std/cpp_lib_complex_udls_14.cpp
	checks/std/cpp_lib_concepts_20.cpp
	checks/std/cpp_lib_constexpr_misc_20.cpp
	checks/std/cpp_lib_constexpr_swap_algorithms_20.cpp
	checks/std/cpp_lib_destroying_delete_20.cpp
	checks/std/cpp_lib_enable_shared_from_this_17.cpp
	checks/std/cpp_lib_erase_if_20.cpp
	checks/std/cpp_lib_exchange_function_14.cpp
	checks/std/cpp_lib_execution_17.cpp
	checks/std/cpp_lib_filesystem_17.cpp
	checks/std/cpp_lib_gcd_lcm_17.cpp
	checks/std/cpp_lib_generic_associative_lookup_14.cpp
	checks/std/cpp_lib_generic_unordered_lookup_20.cpp
	checks/std/cpp_lib_hardware_interference_size_17.cpp
	checks/std/cpp_lib_has_unique_object_representations_17.cpp
	checks/std/cpp_lib_hypot_17.cpp
	checks/std/cpp_lib_incomplete_container_elements_17.cpp
	checks/std/cpp_lib_integer_sequence_14.cpp
	checks/std/cpp_lib_integral_constant_callable_14.cpp
	checks/std/cpp_lib_invoke_17.cpp
	checks/std/cpp_lib_is_aggregate_17.cpp
	checks/std/cpp_lib_is_constant_evaluated_20.cpp
	checks/std/cpp_lib_is_final_14.cpp
	checks/std/cpp_lib_is_invocable_17.cpp
	checks/std/cpp_lib_is_null_pointer_14.cpp
	checks/std/cpp_lib_is_swappable_17.cpp
	checks/std/cpp_lib_launder_17.cpp
	checks/std/cpp_lib_list_remove_return_type_20.cpp
	checks/std/cpp_lib_logical_traits_17.cpp
	checks/std/cpp_lib_make_from_tuple_17.cpp
	checks/std/cpp_lib_make_reverse_iterator_14.cpp
	checks/std/cpp_lib_make_unique_14.cpp
	checks/std/cpp_lib_map_try_emplace_17.cpp
	checks/std/cpp_lib_math_special_functions_17.cpp
	checks/std/cpp_lib_memory_resource_17.cpp
	checks/std/cpp_lib_node_extract_17.cpp
	checks/std/cpp_lib_nonmember_container_access_17.cpp
	checks/std/cpp_lib_not_fn_17.cpp
	checks/std/cpp_lib_null_iterators_14.cpp
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	checks/std/cpp_lib_parallel_algorithm_17.cpp
	checks/std/cpp_lib_quoted_string_io_14.cpp
	checks/std/cpp_lib_ranges_20.cpp
	checks/std/cpp_lib_raw_memory_algorithms_17.cpp
	checks/std/cpp_lib_result_of_sfinae_14.cpp
	checks/std/cpp_lib_robust_nonmodifying_seq_ops_14.cpp
	checks/std/cpp_lib_sample_17.cpp
	checks/std/cpp_lib_scoped_lock_17.cpp
	checks/std/cpp_lib_shared_mutex_17.cpp
	checks/std/cpp_lib_shared_ptr_arrays_17.cpp
	checks/std/cpp_lib_shared_ptr_weak_type_17.cpp
	checks/std/cpp_lib_shared_timed_mutex_14.cpp
	checks/std/cpp_lib_string_udls_14.cpp
	checks/std/cpp_lib_string_view_17.cpp
	checks/std/cpp_lib_three_way_comparison_20.cpp
	checks/std/cpp_lib_to_chars_17.cpp
	checks/std/cpp_lib_transformation_trait_aliases_14.cpp
	checks/std/cpp_lib_transparent_operators_14.cpp
	checks/std/cpp_lib_transparent_operators_17.cpp
	checks/std/cpp_lib_tuple_element_t_14.cpp
	checks/std/cpp_lib_tuples_by_type_14.cpp
	checks/std/cpp_lib_type_trait_variable_templates_17.cpp
	checks/std/cpp_lib_uncaught_exceptions_17.cpp
	checks/std/cpp_lib_unordered_map_try_emplace_17.cpp
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	checks/std/cpp_nsdmi_11.cpp
	checks/std/cpp_range_based_for_11.cpp
	checks/std/cpp_range_based_for_17.cpp
	checks/std/cpp_raw_strings_11.cpp
	checks/std/cpp_ref_qualifiers_11.cpp
	checks/std/cpp_return_type_deduction_14.cpp
	checks/std/cpp_rtti_03.cpp
	checks/std/cpp_rvalue_references_11.cpp
	checks/std/cpp_sized_deallocation_14.cpp
	checks/std/cpp_static_assert_11.cpp
	checks/std/cpp_static_assert_17.cpp
	checks/std/cpp_structured_bindings_17.cpp
	checks/std/cpp_template_template_args_17.cpp
	checks/std/cpp_threadsafe_static_init_11.cpp
	checks/std/cpp_unicode_characters_11.cpp
	checks/std/cpp_unicode_literals_11.cpp
	checks/std/cpp_user_defined_literals_11.cpp
	checks/std/cpp_variable_templates_14.cpp
	checks/std/cpp_variadic_templates_11.cpp
	checks/std/cpp_variadic_using_17.cpp
	checks/test_case.cpp
	doc/html/index.html
	test/all/Jamfile.v2
	test/config_info.cpp
	test/config_test.cpp

doc/macro_reference.qbk

@@ -1056,6 +1056,31 @@ provide compliant C++17 support.
 
 [endsect]
 
+[section Macros that describe C++20 features not supported]
+
+The following macros describe features in the 2020 ISO C++ standard, formerly known as C++2a,
+that are not yet supported by a particular compiler or library.
+
+[table
+[[Macro ][Description ]]
+[[`BOOST_NO_CXX20_HDR_BARRIER`][The compiler does not support the header `<barrier>`.]]
+[[`BOOST_NO_CXX20_HDR_FORMAT`][The compiler does not support the header `<format>`.]]
+[[`BOOST_NO_CXX20_HDR_SOURCE_LOCATION`][The compiler does not support the header `<format>`.]]
+[[`BOOST_NO_CXX20_HDR_BIT`][The compiler does not support the header `<bit>`.]]
+[[`BOOST_NO_CXX20_HDR_LATCH`][The compiler does not support the header `<latch>`.]]
+[[`BOOST_NO_CXX20_HDR_SPAN`][The compiler does not support the header `<span>`.]]
+[[`BOOST_NO_CXX20_HDR_COMPARE`][The compiler does not support the header `<compare>`.]]
+[[`BOOST_NO_CXX20_HDR_NUMBERS`][The compiler does not support the header `<numbers>`.]]
+[[`BOOST_NO_CXX20_HDR_STOP_TOKEN`][The compiler does not support the header `<stop_token>`.]]
+[[`BOOST_NO_CXX20_HDR_CONCEPTS`][The compiler does not support the header `<concepts>`.]]
+[[`BOOST_NO_CXX20_HDR_RANGES`][The compiler does not support the header `<range>`.]]
+[[`BOOST_NO_CXX20_HDR_SYNCSTREAM`][The compiler does not support the header `<syncstream>`.]]
+[[`BOOST_NO_CXX20_HDR_COROUTINE`][The compiler does not support the header `<coroutine>`.]]
+[[`BOOST_NO_CXX20_HDR_SEMAPHORE`][The compiler does not support the header `<semaphore>`.]]
+]
+
+[endsect]
+
 [section Macros that describe features that have been removed from the standard.]
 
 The following macros describe features which were required by one version of the standard, but have been removed by later versions.
@@ -1066,6 +1091,7 @@ The following macros describe features which were required by one version of the
 [[`BOOST_NO_AUTO_PTR`][The standard library no longer supports `std::auto_ptr`. It was deprecated in C++11 and is removed from C++14.]]
 [[`BOOST_NO_CXX98_FUNCTION_BASE`][The standard library no longer supports `std::unary_function` and `std::binary_function`. They were deprecated in C++11 and is removed from C++14.]]
 [[`BOOST_NO_CXX98_BINDERS`][The standard library no longer supports `std::bind1st`, `std::bind2nd`, `std::ptr_fun` and `std::mem_fun`. They were deprecated in C++11 and is removed from C++14.]]
+[[`BOOST_NO_CXX11_ATOMIC_SMART_PTR`][The standard library no longer supports atomic overloads for `std::shared_ptr`: use `std::atomic<shared_ptr<T>>` instead.]]
 ]
 
 [endsect]