Some compiler provided type traits like __has_trivial_constructor have been documented
as deprecated for quite some time.
Still, some people apparently still use them, even though mixing them with concepts
and with deleted functions leads to weird results. There's also disagreement about some
edge cases between GCC (which Clang claims to follow) and MSVC.
This patch adds deprecation warnings for the usage of those builtins, except for __has_trivial_destructor
which doesn't have a GCC alternative.
I made the warning on by default, so I had to silence it for some tests but it's not too many.
Some (decade old) history of issues with those builtins:
The abseil usage of them that triggered me to add this warning:
Weird interaction of those builtins with C++20's conditionally trivial special member functions: