MS-Windows followup for 2012-11-14T04:55:41Z!eggert@cs.ucla.edu, regarding faccessat.

MS-Windows followup for 2012-11-14T04:55:41Z!eggert@cs.ucla.edu, regarding faccessat.

 nt/inc/unistd.h (faccessat): Add prototype.
 (AT_FDCWD, AT_EACCESS, AT_SYMLINK_NOFOLLOW): New macros; the first
 2 moved from ms-w32.h.
 nt/inc/ms-w32.h (AT_FDCWD, AT_EACCESS, faccessat): Remove macros.

 src/w32.c (faccessat): Rename from sys_faccessat.  (No need to use a
 different name, as the MS runtime does not have such a function,
 and probably never will.)  All callers changed.  Ignore DIRFD
 value if PATH is an absolute file name, to match Posix spec
 better.  If AT_SYMLINK_NOFOLLOW is set in FLAGS, don't resolve
 symlinks.

Fixes: debbugs:12632