Make strtok benchmark competive.

We include a generic version of strtok to result which could be faster
when underlying primitives are better optimized than current version.

string/strtok.c

@@ -22,6 +22,10 @@ static char *olds;
 
 #undef strtok
 
+#ifndef STRTOK
+# define STRTOK strtok
+#endif
+
 /* Parse S into tokens separated by characters in DELIM.
    If S is NULL, the last string strtok() was called with is
    used.  For example:
@@ -32,7 +36,7 @@ static char *olds;
 		// s = "abc\0=-def\0"
 */
 char *
-strtok (s, delim)
+STRTOK (s, delim)
      char *s;
      const char *delim;
 {