opendir, closedir, dirfd, fdopendir: port to OS/2 kLIBC

opendir, closedir, dirfd, fdopendir: port to OS/2 kLIBC

* lib/closedir.c (closedir): Unregister fd if closedir() succeeds.
* lib/dirent.in.h (_gl_register_dirp_fd, _gl_unregister_dirp_fd):
Declare on kLIBC.
* lib/dirfd.c (struct dirp_fd_list): New. Structures to keep track of
fd associated with dirp.
(_gl_register_dirp_fd): New. Register fd associated with dirp to
dirp_fd_list.
(_gl_unregister_dirp_fd): New. Unregister fd with closing it.
(dirfd): Implemented for kLIBC.
* lib/fdopendir.c (fdopendir): Implemented for kLIBC.
* lib/opendir.c (opendir): New. Register fd and dirp pair if open()
succeeds.
* m4/closedir.m4 (gl_FUNC_CLOSEDIR): Replace if OS/2.
* m4/dirfd.m4 (gl_FUNC_DIRFD): Likewise.
(REPLACE_DIRFD): Define to 1 if replaced.
* m4/opendir.m4 (gl_FUNC_OPENDIR): Likewise.
* modules/closedir (Depends-on): Add dirfd.
* modules/dirfd (Depends-on): Add 'test $REPLACE_DIRFD = 1' to errno
condition.
(configure.ac): Add dirfd to LIBOBJS if $REPLACE_DIRFD = 1 as well.
* modules/opendir (Depends-on): Add dirfd.