/* Call readlink to get the symbolic link value of FILENAME.
Return a pointer to that NUL-terminated string in malloc'd storage.
If readlink fails, return NULL (caller may use errno to diagnose).
- If realloc fails, or if the link value is longer than SIZE_MAX :-),
+ If malloc fails, or if the link value is longer than SSIZE_MAX :-),
give a diagnostic and exit. */
char *