Prepare shared_ptr for array support

Prepare shared_ptr for array support

	* include/backward/auto_ptr.h (__shared_ptr(auto_ptr&&))
	(shared_ptr(auto_ptr&&)): Adjust template parameter lists.
	* include/bits/shared_ptr.h (__sp_compatible_with)
	(__sp_is_constructible): New helper traits for shared_ptr.
	(shared_ptr::_Convertible): Replace with _Constructible.
	(shared_ptr::_Constructible, shared_ptr::_Assignable): Forward checks
	to base class.
	(shared_ptr::shared_ptr, shared_ptr::operator=): Constrain template
	with _Constructible and _Assignable.
	(shared_ptr::shared_ptr(shared_ptr<_Tp1>, _Tp*)): Use element_type
	instead of _Tp.
	(operator<): Likewise.
	(operator>): Define in terms of operator<.
	(static_pointer_cast, const_pointer_cast, dynamic_pointer_cast): Use
	element_type instead of _Tp.
	(reinterpret_pointer_cast): Define for C++17.
	(weak_ptr::_Convertible): Replace with _Constructible.
	(weak_ptr::_Constructible, weak_ptr::_Assignable): Forward checks
	to base class.
	(weak_ptr::weak_ptr, weak_ptr::operator=): Constrain templates
	with _Constructible and _Assignable.
	* include/bits/shared_ptr_base.h (__shared_ptr::_Convertible): Replace
	with _Compatible.
	(__shared_ptr::_SafeConv): New constraint for incoming raw pointers.
	(__shared_ptr::_Compatible): New constraint for converting from
	other types of shared_ptr and weak_ptr.
	(__shared_ptr::_Assignable): Define in terms of _Compatible.
	(__shared_ptr::_UniqCompatible, __shared_ptr::_UniqAssignable): New
	constraints for converting from unique_ptr.
	(__shared_ptr::__shared_ptr, __shared_ptr::operator=): Constrain
	template with _SaveConf, _Compatible and _Assignable. Remove
	__glibcxx_function_requires concept checks. Add static assertion for
	deleter expression being well-formed.
	(__shared_ptr::__shared_ptr(__shared_ptr<_Tp1>, _Tp*))
	(__shared_ptr::operator*, __shared_ptr::operator->)
	(__shared_ptr::get, __shared_ptr::_M_ptr): Use element_type instead
	of _Tp.
	(operator<): Likewise.
	(operator>): Define in terms of operator<.
	(static_pointer_cast, const_pointer_cast, dynamic_pointer_cast): Use
	element_type instead of _Tp.
	(reinterpret_pointer_cast): Define for C++17.
	(weak_ptr::_Convertible): Replace with _Compatible.
	(weak_ptr::_Compatible, weak_ptr::_Assignable): New constraints for
	conversions from other types of weak_ptr and shared_ptr.
	(__weak_ptr::__weak_ptr, __weak_ptr::operator=): Constrain templates
	with _Constructible and _Assignable.
	(__weak_ptr::_M_ptr): Use element_type instead of _Tp.
	* testsuite/20_util/shared_ptr/assign/auto_ptr_neg.cc: Adjust
	dg-error pattern.
	* testsuite/20_util/shared_ptr/cons/auto_ptr.cc: Test conversions.
	* testsuite/20_util/shared_ptr/cons/unique_ptr.cc: Likewise.
	* testsuite/20_util/shared_ptr/cons/void_neg.cc: Likewise.
	* testsuite/20_util/shared_ptr/casts/reinterpret.cc: New test.

From-SVN: r241373