getopt: annotate files with relationship to gnulib.

getopt: annotate files with relationship to gnulib.

As the final act in this patchset, adjust the "This file is part of
the GNU C Library" message at the top of each file to indicate which
files are synced with gnulib.

	* posix/bits/getopt_core.h, posix/bits/getopt_ext.h
	* posix/getopt.c, posix/getopt1.c, posix/getopt_int.h:
	Mention in top-of-file boilerplate that these files are shared
	with gnulib.
	* posix/getopt.h, posix/bits/getopt_posix.h:
	Mention in top-of-file boilerplate that these files are NOT shared
	with gnulib, unlike the rest of the getopt implementation.