Remove access to legacy time zone support in gettimeofday etc.

Remove access to legacy time zone support in gettimeofday etc.

gettimeofday and ftime are not quite fully implementable on systems
that only provide a primitive equivalent to clock_gettime, because
they can also report information about a system-wide time zone.  This
mechanism has been deprecated for many years because it can only be
configured on a system-wide basis, and because it only supports the
simplest kinds of daylight-savings rules, but we’ve supported it on a
best-effort basis until now.  This patch removes our support for it:

 * The type 'struct timezone' is still declared as a complete type in
   <sys/time.h>, but code that uses its fields (tz_minuteswest and
   tz_dsttime) will not compile.

 * Similarly, code that uses the 'timezone' and 'dstflag' fields of
   struct timeb will not compile anymore.  (This is a willful
   violation of the older iterations of XPG that included
   sys/timeb.h; the relevant conformance tests are XFAILed.)

 * Old binaries that pass a non-NULL 'tzp' pointer to gettimeofday
   will always receive a 'struct timezone' whose tz_minuteswest and
   tz_dsttime fields are zero (as if the system were operating on UTC).

 * Similarly, old binaries that call ftime will always receive a
   'struct timeb' whose timezone and dstflag fields are zero.

 * If the 'tzp' argument to settimeofday is not NULL, the call will fail
   and set errno to ENOSYS.  (This was already the case on the Hurd.)

 * glibc will always pass a second argument of NULL when invoking a
   kernel-provided gettimeofday.

 * On Alpha, the compat symbols gettimeofday@GLIBC_2.0 and
   settimeofday@GLIBC_2.0 (which used 32-bit time_t) now convert
   their arguments and call system primitives that use 64-bit time_t,
   instead of invoking legacy “osf” system calls.

ChangeLog:

	* time/sys/time.h (struct timezone): Remove tz_minuteswest
	and tz_dsttime fields; replace with padding to preserve the size.
	* time/sys/timeb.h (struct timeb): Remove timezone and dstflag
	fields; replace with padding to preserve the size.
	* conform/Makefile: XFAIL tests because struct timeb is no longer
	fully conformant with Unix98.

	* sysdeps/posix/gettimeofday.c
	* sysdeps/unix/sysv/linux/gettimeofday.c
	* sysdeps/unix/sysv/linux/aarch64/gettimeofday.c
	* sysdeps/unix/sysv/linux/powerpc/gettimeofday.c
	* sysdeps/unix/sysv/linux/x86/gettimeofday.c
	(gettimeofday): When ‘tz’ argument is not NULL, just clear it.
	Always pass a null pointer as the second argument to a
	gettimeofday (v)syscall.

	* sysdeps/unix/bsd/ftime.c: Unconditionally clear the memory that
	was formerly the ‘timezone’ and ‘dstflag’ fields of struct timeb.

	* sysdeps/unix/syscalls.list: Remove entry for settimeofday.
	* sysdeps/unix/settimeofday.c: New file.
	(settimeofday): Fail with ENOSYS if ‘tz’ argument is not NULL.

	* sysdeps/unix/sysv/linux/alpha/syscalls.list: Remove entries for
        osf_gettimeofday, osf_settimeofday, and settimeofday.
	* sysdeps/unix/sysv/linux/alpha/osf_gettimeofday.c:
	New file.  Call the 64-bit gettimeofday, then convert to a
	32-bit struct timeval.  On overflow, saturate the struct timeval
	and fail with EOVERFLOW.
	* sysdeps/unix/sysv/linux/alpha/osf_settimeofday.c: New file.
        Convert to a 64-bit struct timeval and call 64-bit settimeofday.
        Fail with ENOSYS if ‘tz’ argument is not NULL.

	* sunrpc/auth_des.c, sunrpc/auth_unix.c
	* sysdeps/posix/time.c, sysdeps/unix/stime.c:
	Remove unnecessary casts of NULL.

	* sysdeps/unix/sysv/linux/powerpc/time.c (time_syscall):
	Use (void *)0 instead of NULL when passing a null pointer
	as an untyped argument.

	* manual/time.texi: Remove documentation of fields of
	struct timezone.  Revise text to further emphasize that
	the second argument to gettimeofday/settimeofday should
	always be a null pointer.