Fix clang 11.0.1 C++17 and prepare C++20 (WIP)v0.8.1

- Make 'to_string(const endian& v)' external, remove constexpr
- Move packed_t from byte_util.hpp -> packed_attribute.hpp w/o endian conversion
  - Note: Using pointer_cast and packed_t actually implements constexpr bit_cast
- Add 'get_value(const packed_t<T>* source, const bool littleEndian) noexcept' to byte_util.hpp
- pointer_cast<> needs to have const removed from underlying pointer type
- uint[128,192,256]_t(const uint8_t v[]): Use '*this = pointer_cast<packed_t<uint128_t>*>( v )->store' as constexpr solution.
  - WIP: Consider making it bitcast!

- ordered_atomic.hpp: Use C++17 aliased enum or C++20 inlince constexpr aliases std::memory_order types

- type_traits_queries.hpp: is_scoped_enum<> is C++23

1 files changed, 12 insertions, 0 deletions

diff --git a/include/jau/packed_attribute.hpp b/include/jau/packed_attribute.hpp
index 54e264c..bd9136d 100644
--- a/include/jau/packed_attribute.hpp
+++ b/include/jau/packed_attribute.hpp
@@ -53,4 +53,16 @@
     #endif
 #endif
 
+    /**
+     * Safe access to a pointer cast from unaligned memory via __packed__ attribute,
+     * i.e. utilizing compiler generated safe load and store operations.
+     * <p>
+     * This template shall cause no costs, the cast data pointer is identical to 'T & p = &store'.
+     * </p>
+     */
+    template<typename T> __pack ( struct packed_t {
+        T store;
+    } ) ;
+
+
 #endif /* PACKED_ATTRIBUTE_HPP_ */