Broken strspn and strpbrk macros

["Joseph S. Myers" <jsm28 at cam dot ac dot uk>]

glibc's <bits/string2.h> strspn and strpbrk macros are broken when the
second string is empty: they fail to evaluate the first string for its
side effects.  This may also apply to the <bits/string.h> versions.

Testcase: compile and run the following with optimization.

#include <string.h>
#include <stdlib.h>
#include <stdio.h>

int
main (void)
{
  const char *a = "abc";
  const char *b = a;
  puts ("Testing strspn.");
  strspn (b++, "");
  if (b != a + 1)
    abort ();
  puts ("Testing strpbrk.");
  strpbrk (b++, "");
  if (b != a + 2)
    abort ();
  exit (0);
}

-- 
Joseph S. Myers
jsm28@cam.ac.uk