Protect zic's symlink() call with #ifdef HAVE_SYMLINK.

The IANA crew seem to think that symlink() exists everywhere nowadays,
and they may well be right.  But we use #ifdef HAVE_SYMLINK elsewhere
so for consistency we should do it here too.  Noted by Michael Paquier.

src/timezone/zic.c

@@ -811,6 +811,7 @@ dolink(char const * fromfield, char const * tofield)
 			link_errno = link(fromname, toname) == 0 ? 0 : errno;
 		if (link_errno != 0)
 		{
+#ifdef HAVE_SYMLINK
 			const char *s = fromfield;
 			const char *t;
 			char	   *p;
@@ -838,6 +839,7 @@ dolink(char const * fromfield, char const * tofield)
 							strerror(link_errno));
 			}
 			else
+#endif   /* HAVE_SYMLINK */
 			{
 				FILE	   *fp,
 						   *tp;