Consolidate non cancellable openat call

This patch consolidates all the non cancellable openat{64} calls to use
the __openat{64}_nocancel identifier.  For non cancellable targets it will
be just a macro to call the default respective symbol while on Linux
will be a internal one.

Checked on x86_64-linux-gnu, x86_64-linux-gnu-x32, and i686-linux-gnu.

	* sysdeps/generic/not-cancel.h (openat_not_cancel): Remove macro.
	(openat_not_cancel_3): Likewise.
	(openat64_not_cancel_3): Likewise).
	(openat_not_cancel_3): Likewise).
	* sysdeps/unix/sysv/linux/not-cancel.h (openat_not_cancel): Remove
	macro.
	(openat_not_cancel_3): Likewise.
	(openat64_not_cancel): Likewise.
	(openat64_not_cancel_3): Likewise.
	* sysdeps/unix/sysv/linux/openat.c (__openat_nocancel): New function.
	* sysdeps/unix/sysv/linux/openat64.c (__openat64_nocancel): Likewise.
	* io/ftw.c (open_dir_stream): Replace openat{64}_not_cancel{_3} with
	__open{64}_nocancel.
	* sysdeps/mach/hurd/opendir.c (__opendirat): Likewise.
	* sysdeps/posix/getcwd.c (__getcwd): Likewise.
	* sysdeps/posix/opendir.c (__opendirat): Likewise.