posix: accept inode 0 is a valid inode number (BZ #19971)

According to this kernel commit 2adc376c55194, d_ino 0 is a regular inode
number on Linux (which also matches POSIX, as it does not treat the value
as special).  This patch makes glob accept is a valid inode number.

This is also a sync with gnulib commit c8e57c1.

Checked on x86_64-linux-gnu and on a build using build-many-glibcs.py
for all major architectures.

	[BZ #1062]
	[BZ #19971]
	* posix/glob.c (struct readdir_result): Remove skip_entry member.
	(readdir_result_skip_entry, D_INO_TO_RESULT): Remove.
	All uses removed.