Introduce NO_RTLD_HIDDEN, make hurd use it instead of NO_HIDDEN

Introduce NO_RTLD_HIDDEN, make hurd use it instead of NO_HIDDEN

On the Hurd, the rtld needs to see its own dumb versions of a few functions
(defined in sysdeps/mach/hurd/dl-sysdep.c) overridden by libc's versions once
loaded. rtld should thus not have hidden attribute for these.  To achieve this,
the Hurd port used to just define NO_HIDDEN, which disables it completely. For
now, this changes that to disabling it for all rtld functions, for simplicity.

See Roland's comment on https://sourceware.org/bugzilla/show_bug.cgi?id=15605#c5

The ld.so numbers remain at

  8 .rel.plt      000000c8  00000c24  00000c24  00000c24  2**2
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
  9 .plt          000001a0  00000cf0  00000cf0  00000cf0  2**4
                  CONTENTS, ALLOC, LOAD, READONLY, CODE
 10 .plt.got      00000010  00000e90  00000e90  00000e90  2**3
                  CONTENTS, ALLOC, LOAD, READONLY, CODE
 18 .got.plt      00000070  0002d000  0002d000  0002c000  2**2
                  CONTENTS, ALLOC, LOAD, DATA

which is about 3 times as much as on Linux.

The libc.so numbers get divided by 3 (the remainings are mostly RPC stub calls)

	* include/libc-symbols.h [NO_RTLD_HIDDEN] (rtld_hidden_proto,
	rtld_hidden_tls_proto, rtld_hidden_def, rtld_hidden_weak,
	rtld_hidden_rtld_hidden_ver, data_def, rtld_hidden_data_weak,
	rtld_hidden_data_ver): Define to empty.
	* include/assert.h [IS_IN(rtld) && NO_RTLD_HIDDEN] (__assert_fail,
	__assert_perror_fail): Likewise.
	* include/dirent.h [IS_IN(rtld) && NO_RTLD_HIDDEN]
	(__rewinddir): Likewise.
	* include/libc-internal.h [IS_IN(rtld) && NO_RTLD_HIDDEN]
	(__profile_frequency): Likewise.
	* include/setjmp.h (__sigsetjmp): Likewise.
	* include/signal.h [IS_IN(rtld) && NO_RTLD_HIDDEN] (__sigaction,
	__libc_sigaction): Likewise.
	* include/stdlib.h [NO_RTLD_HIDDEN] (unsetenv, __strtoul_internal): Do
	not set hidden attribute.
	* include/string.h [IS_IN(rtld) && NO_RTLD_HIDDEN] (__stpcpy, __strdup,
	__strerror_t, __strsep_g, memchr, memcmp, memcpy, memmove, memset,
	rawmemchr, stpcpy, strchr, strcmp, strlen, strnlen, strsep): Likewise.
	* include/sys/stat.h [IS_IN(rtld) && NO_RTLD_HIDDEN] (__fxstat,
	__fxstat64, __lxstat, __lxstat64, __xstat, __xstat64,
	__fxstatat64): Likewise.
	* include/sys/utsname.h [IS_IN(rtld) && NO_RTLD_HIDDEN]
	(__uname): Likewise.
	* include/sysdeps/generic/_itoa.h [IS_IN(rtld) && NO_RTLD_HIDDEN]
	(_itoa_upper_digits, _itoa_lower_digits): Likewise.
	* sysdeps/mach/hurd/configure.ac (NO_HIDDEN): Do not set.
	(NO_RTLD_HIDDEN): Set.
	* sysdeps/mach/hurd/configure: Refresh.
	* config.h.in: Refresh.