libstdc++: Fix -Wsystem-headers warnings

Fix some problems noticed with -Wsystem-headers.

libstdc++-v3/ChangeLog:

	* include/bits/stl_tempbuf.h (_Temporary_buffer): Disable
	warnings about get_temporary_buffer being deprecated.
	* include/ext/functional (mem_fun1, mem_fun1_ref): Disable
	warnings about mem_fun1_t, const_mem_fun1_t, mem_fun1_ref_t and
	const_mem_fun1_ref_t being deprecated.
	* include/std/array (__array_traits<T, 0>): Remove artificial
	attributes which give warnings about being ignored.
	* include/std/spanstream (basic_spanbuf::setbuf): Add assertion
	and adjust to avoid narrowing warning.
	* libsupc++/exception_ptr.h [!__cpp_rtti && !__cpp_exceptions]
	(make_exception_ptr): Add missing inline specifier.