[HAVE_LIBGEN_H]: Include <libgen.h>, for

[HAVE_LIBGEN_H]: Include <libgen.h>, for
eaccess on Solaris and SVR4-like systems.
(euidaccess): Use HAVE_EACCESS, not HAVE_DECL_EACCESS.
[!defined LIBC]: Included group-member.h, stat-macros.h.
(S_IXUSR, S_IXGRP, S_IXOTH, S_IROTH, S_IWOTH, S_IXOTH):
Remove; now done by stat-macros.h.
(NGROUPS_MAX, group_member): Remove; now done by group-member.h.
No need to include <limits.h>.
(errno): Remove decl; we now assume C89 or better.
(access, getuid, getgid, geteuid, getegid, stat) [defined _LIBC]:
New macros.
(uid, gid, have_ids): Remove these static variables.
They weren't accurate for programs that also invoked setreuid etc.
(euidaccess) [defined EFF_ONLY_OK || defined ACC_SELF ||
HAVE_DECL_EACCSS]: Use builtin substitutes.
[defined _LIBC]: Ignore __libc_enable_secure; it's not a
correct optimization for programs run as root that later
invoke setreuid.
[no builtin substitutes && HAVE_DECL_SETREGID &&
PREFER_NONREENTRANT_EUIDACCESS]:
Use setreuid+setregid to get the correct answer.
[no builtin substitutes && ! (HAVE_DECL_SETREGID &&
PREFER_NONREENTRANT_EUIDACCESS)]:
Don't assume that the stat macros have their historical values,
as POSIX doesn't require this.
[defined TEST]: Include <stdlib.h>; don't include errno.h
twice; include <error.h> rather than "error.h".