Without this patch, the MH test suite would fail when building with
glibc 2.26, with 'ali' segfaulting like this:

  Core was generated by `/tmp/guix-build-mailutils-3.4.drv-0/mailutils-3.4/mh/.libs/ali -a ./Mail/mh_ali'.
  Program terminated with signal SIGSEGV, Segmentation fault.
  #0  0x00007f8eac263a14 in hash (
      name=0x72642e342e332d73 <error: Cannot access memory at address 0x72642e342e332d73>, hash_num=0) at assoc.c:102
  102	  for (i = 0; *name; name++)
  (gdb) bt
  #0  0x00007f8eac263a14 in hash (
      name=0x72642e342e332d73 <error: Cannot access memory at address 0x72642e342e332d73>, hash_num=0) at assoc.c:102
  #1  0x00007f8eac263e6b in assoc_find_slot (assoc=0xaa59e0, 
      name=0x72642e342e332d73 <error: Cannot access memory at address 0x72642e342e332d73>, install=0x0, slot=0x7ffcddcbf2b8) at assoc.c:219
  #2  0x00007f8eac264124 in mu_assoc_lookup (assoc=0xaa59e0, 
      name=0x72642e342e332d73 <error: Cannot access memory at address 0x72642e342e332d73>, dataptr=0x7ffcdd</td></tr></table>
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