libstdc++: Stop using std::__is_pointer in <deque> and <algorithm> [PR115497]

libstdc++: Stop using std::__is_pointer in <deque> and <algorithm> [PR115497]

This replaces all uses of the std::__is_pointer type trait with uses of
the new __is_pointer built-in. Since the class template was only used to
enable some performance optimizations for algorithms, we can use the
built-in when __has_builtin(__is_pointer) is true (which is the case for
GCC trunk and for current versions of Clang) and just forego the
optimization otherwise.

Removing the uses of std::__is_pointer means it can be removed from
<bits/cpp_type_traits.h>, which is another step towards fixing PR
115497.

libstdc++-v3/ChangeLog:

	PR libstdc++/115497
	* include/bits/deque.tcc (__lex_cmp_dit): Replace __is_pointer
	class template with __is_pointer(T) built-in.
	(__lexicographical_compare_aux1): Likewise.
	* include/bits/stl_algobase.h (__equal_aux1): Likewise.
	(__lexicographical_compare_aux1): Likewise.