libstdc++: Replace some uses of std::__addressof with std::addressof

libstdc++: Replace some uses of std::__addressof with std::addressof

Since r16-154-gc91eb5a5c13f14 std::addressof is no less efficient than
std::__addressof, so change some uses of the latter to the former.  We
can't change them all, because some uses need to compile as C++98 which
only has std::__addressof.

Similarly, since r16-848-gb2aeeb2803f97b std::is_constant_evaluated is
no less efficient than std::__is_constant_evaluated.

libstdc++-v3/ChangeLog:

	* include/bits/stl_construct.h: Replace std::__addressof with
	std::addressof in code that doesn't need to compile as C++98.
	Replace std::__is_constant_evaluated with
	std::is_constant_evaluated in code that doesn't need to compile
	as C++17 or earlier.
	* include/bits/stl_uninitialized.h: Likewise for __addressof.