package/diffutils: bump to version 3.8

package/diffutils: bump to version 3.8

- Update indentation in hash file (two spaces)
- Fix the following build failure with glibc 2.34 thanks to
  https://git.savannah.gnu.org/cgit/diffutils.git/commit/?id=498f88de4de761c1b5741fd8c78d4f5db9f3ce8b
  https://git.savannah.gnu.org/cgit/gnulib.git/commit/?id=f9e2b20a12a230efa30f1d479563ae07d276a94b

In file included from /home/giuliobenetti/autobuild/run/instance-0/output-1/host/arc-buildroot-linux-gnu/sysroot/usr/include/signal.h:328,
                 from ./signal.h:52,
                 from c-stack.c:49:
c-stack.c:55:26: error: missing binary operator before token "("
   55 | #elif HAVE_LIBSIGSEGV && SIGSTKSZ < 16384
      |                          ^~~~~~~~

https://savannah.gnu.org/forum/forum.php?forum_id=10031

Fixes:
 - http://autobuild.buildroot.org/results/6abde124e3124932d3c14d3b699f0572a2f4632d

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>