Remove ia64-linux-gnu

Linux 6.7 removed ia64 from the official tree [1], following the general
principle that a glibc port needs upstream support for the architecture
in all the components it depends on (binutils, GCC, and the Linux
kernel).

Apart from the removal of sysdeps/ia64 and sysdeps/unix/sysv/linux/ia64,
there are updates to various comments referencing ia64 for which removal
of those references seemed appropriate. The configuration is removed
from README and build-many-glibcs.py.

The CONTRIBUTED-BY, elf/elf.h, manual/contrib.texi (the porting
mention), *.po files, config.guess, and longlong.h are not changed.

For Linux it allows cleanup some clone2 support on multiple files.

The following bug can be closed as WONTFIX: BZ 22634 [2], BZ 14250 [3],
BZ 21634 [4], BZ 10163 [5], BZ 16401 [6], and BZ 11585 [7].

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=43ff221426d33db909f7159fdf620c3b052e2d1c
[2] https://sourceware.org/bugzilla/show_bug.cgi?id=22634
[3] https://sourceware.org/bugzilla/show_bug.cgi?id=14250
[4] https://sourceware.org/bugzilla/show_bug.cgi?id=21634
[5] https://sourceware.org/bugzilla/show_bug.cgi?id=10163
[6] https://sourceware.org/bugzilla/show_bug.cgi?id=16401
[7] https://sourceware.org/bugzilla/show_bug.cgi?id=11585
Reviewed-by: Carlos O'Donell <carlos@redhat.com>

sysdeps/unix/sysv/linux/fstat64.c

@@ -31,7 +31,7 @@ __fstat64_time64 (int fd, struct __stat64_t64 *buf)
 #if !FSTATAT_USE_STATX
 # if XSTAT_IS_XSTAT64
 #  ifdef __NR_fstat
-  /* 64-bit kABI, e.g. aarch64, ia64, powerpc64*, s390x, riscv64, and
+  /* 64-bit kABI, e.g. aarch64, powerpc64*, s390x, riscv64, and
      x86_64.  */
   return INLINE_SYSCALL_CALL (fstat, fd, buf);
 #  elif defined __NR_fstat64