lib: Add strtok() and strtok_r()

Add strtok() and strtok_r() to the library.

Signed-off-by: Harshit Sharma <harshitsharmajs@gmail.com>
Change-Id: Ic855b31669be1c274cbf247c53ffa6f74ec5bf35
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41420
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Werner Zeh <werner.zeh@siemens.com>

src/include/string.h

@@ -29,6 +29,8 @@ int strcmp(const char *s1, const char *s2);
 int strncmp(const char *s1, const char *s2, int maxlen);
 int strspn(const char *str, const char *spn);
 int strcspn(const char *str, const char *spn);
+char *strtok_r(char *str, const char *delim, char **ptr);
+char *strtok(char *str, const char *delim);
 long atol(const char *str);
 
 /**