Due to PR c++/85723 the std::is_trivial trait is true for types with a
deleted default constructor, so the use of std::is_trivial in
std::to_array is not sufficient to ensure the type can be trivially
default constructed then filled using memcpy.
I also forgot that a type with a deleted assignment operator can still
be trivial, so we also need to check that it's assignable because the
is_constant_evaluated() path can't use memcpy.
Replace the uses of std::is_trivial with std::is_trivially_copyable
(needed for memcpy), std::is_trivially_default_constructible (needed so
that the default construction is valid and does no work) and
std::is_copy_assignable (needed for the constant evaluation case).
libstdc++-v3/ChangeLog:
PR libstdc++/115522
* include/std/array (to_array): Workaround the fact that
std::is_trivial is not sufficient to check that a type is
trivially default constructible and assignable.
* testsuite/23_containers/array/creation/115522.cc: New test.
(cherry picked from commit 510ce5eed69ee1bea9c2c696fe3b2301e16d1486)
21c8708ba6