With the new value of __cpp_concepts required by P2493, we can test
whether the compiler supports conditionally trivial special members.
This allows us to remove the workaround that disables fully-constexpr
std::variant for Clang. Now it should work for non-GCC compilers (such
as future releases of Clang) that support conditionally trivial
destructors and define the new value of __cpp_concepts.
libstdc++-v3/ChangeLog:
PR libstdc++/103891
* include/bits/c++config (_GLIBCXX_HAVE_COND_TRIVIAL_SPECIAL_MEMBERS):
Remove.
* include/std/variant: Check feature test macros instead.
* include/std/version: Likewise.
164a761a9f