Use faccessat, not access, when checking file permissions.

Use faccessat, not access, when checking file permissions.

* .bzrignore: Add lib/fcntl.h.
* configure.ac (euidaccess): Remove check; gnulib does this for us now.
(gl_FCNTL_O_FLAGS): Define a dummy version.
* lib/at-func.c, lib/euidaccess.c, lib/faccessat.c, lib/fcntl.in.h:
* lib/getgroups.c, lib/group-member.c, lib/root-uid.h:
* lib/xalloc-oversized.h, m4/euidaccess.m4, m4/faccessat.m4:
* m4/fcntl_h.m4, m4/getgroups.m4, m4/group-member.m4:
New files, from gnulib.
* lib/gnulib.mk, m4/gnulib-comp.m4: Regenerate.
* admin/merge-gnulib (GNULIB_MODULES): Add faccessat.
(GNULIB_TOOL_FLAGS): Avoid at-internal, fchdir, malloc-posix,
openat-die, openat-h, save-cwd.  Do not avoid fcntl-h.
Omit gnulib's m4/fcntl-o.m4.
* nt/inc/ms-w32.h (AT_FDCWD, AT_EACCESS): New symbols.
(access): Remove.
(faccessat): New macro.
* src/Makefile.in (LIB_EACCESS): New macro.
(LIBES): Use it.
* src/callproc.c (init_callproc):
* src/charset.c (init_charset):
* src/fileio.c (check_existing, check_executable):
* src/lread.c (openp, load_path_check):
* src/process.c (allocate_pty):
* src/xrdb.c (file_p):
Use faccessat, not access or euidaccess.  Use symbolic names
instead of integers for the flags, as they're portable now.
* src/charset.c, src/xrdb.c: Include <fcntl.h>, for the new flags used.
* src/fileio.c (Ffile_readable_p):
Use faccessat, not stat + open + close.
(file_directory_p): New function, which uses 'stat' on most places
but 'access' (for efficiency) if WINDOWSNT.
* src/fileio.c (Ffile_directory_p, Fset_file_times):
* src/xrdb.c (file_p): Use file_directory_p.
* src/lisp.h (file_directory_p): New decl.
* src/lread.c (openp): When opening a file, use fstat rather than
stat, as that avoids a permissions race.  When not opening a file,
use file_directory_p rather than stat.
* src/process.c, src/sysdep.c, src/term.c: All uses of '#ifdef O_NONBLOCK'
changed to '#if O_NONBLOCK', to accommodate gnulib O_* tyle.
* src/w32.c (sys_faccessat): Rename from sys_access and switch to
faccessat's API.  All uses changed.

Fixes: debbugs:12632