Remove __need macros from stdio.h and wchar.h.

Remove __need macros from stdio.h and wchar.h.

wint_t is a little finicky because it might be defined by stddef.h, which
belongs to the compiler.

In addition to the _types_, a bunch of other declarations shared between
wctype.h and wchar.h are factored out to their own header.

	* libio/bits/types/FILE.h, libio/bits/types/__FILE.h
	* wcsmbs/bits/types/mbstate_t.h, wcsmbs/bits/types/__mbstate_t.h
	* wcsmbs/bits/types/wint_t.h: New single-type definition files.
	* wctype/bits/wctype-wchar.h: New file holding declarations shared
	between wctype.h and wchar.h.

	* libio/Makefile, wcsmbs/Makefile, wctype/Makefile:
	Install them.

	* include/bits/types/FILE.h, include/bits/types/__FILE.h
	* include/bits/types/mbstate_t.h, include/bits/types/__mbstate_t.h
	* include/bits/types/wint_t.h, include/bits/wcsmbs-wchar.h:
	New wrappers.
	* include/stdio.h, include/wchar.h, include/wctype.h:
	No need to handle __need macros.

	* grp/grp.h, gshadow/gshadow.h, hurd/hurd.h, iconv/gconv.h
	* libio/stdio.h, mach/mach.h, misc/mntent.h, pwd/pwd.h
	* shadow/shadow.h, stdio-common/printf.h, wcsmbs/uchar.h
	* wcsmbs/wchar.h, wctype/wctype.h
	* sysdeps/generic/_G_config.h, sysdeps/unix/sysv/linux/_G_config.h
	Use the new files instead of __need macros.