Assume POSIX 1003.1-1988 or later for unistd.h.

Assume POSIX 1003.1-1988 or later for unistd.h.

* admin/CPP-DEFINES (BROKEN_GETWD, HAVE_GETCWD, HAVE_GETWD, HAVE_SIZE_T)
(HAVE_UNISTD_H): Remove.
* configure.ac: Do not check for getcwd or getwd.
* lib-src/emacsclient.c (getcwd): Remove decl.
(get_current_dir_name): Assume getcwd exists.
* lib-src/etags.c (HAVE_GETCWD): Remove.
(getcwd): Remove decl.
(NO_LONG_OPTIONS): Remove this.  All uses removed.
Emacs always has GNU getopt.
(etags_getcwd): Assume getcwd exists.
* lib-src/movemail.c (F_OK, X_OK, W_OK, R_OK): Remove.
* nt/config.nt (HAVE_GETCWD): Remove.
* src/alloc.c: Assume unistd.h exists.
* src/fileio.c (Fexpand_file_name) [DOS_NT]: Use getcwd, not getwd.
* src/sysdep.c (get_current_dir_name): Assume getcwd exists.
(getwd) [USG]: Remove; no longer needed.
(sys_subshell) [DOS_NT]: Use getcwd, not getwd.
* src/w32.c (getcwd): Rename from getwd, and switch to getcwd's API.
* src/w32.h (getcwd): Remove decl.

Fixes: debbugs:12945