cf: Restore AC_KRB_PROG_YACC to life

Using `AC_PROG_YACC` means accepting that `bison` gets invoked in yacc
compatibility mode (i.e., with the `-y` command-line option).  In recent
versions Bison has started to warn about use of Bison extensions when in
yacc compatibility mode -- even for things yacc itself accepts but which
it doesn't document.

I've confirmed that `bison -d` and `byacc -d` both work for the ASN.1
compiler.

cf/krb-prog-yacc.m4

@@ -1,12 +1,18 @@
 dnl $Id$
 dnl
 dnl
-dnl We prefer byacc or yacc because they do not use `alloca'
+dnl OLD: We prefer byacc or yacc because they do not use `alloca'
+dnl
+dnl CURRENT: We don't mind `alloca', but we do mind `bison -y' because
+dnl          newer versions of `bison', with `-y' complain about %expect and
+dnl          anything that yacc didn't document.  Because `bison' typically
+dnl          also installs a `yacc' link that acts like `bison y', we put
+dnl          `yacc' last in this list.
 dnl
 
 AC_DEFUN([AC_KRB_PROG_YACC],
-[AC_CHECK_PROGS(YACC, byacc yacc 'bison -y')
+[AC_CHECK_PROGS(YACC, 'bison -d' 'byacc -d' yacc)
 if test "$YACC" = ""; then
-  AC_MSG_WARN([yacc not found - some stuff will not build])
+  AC_MSG_WARN([byacc and bison not found - some stuff will not build])
 fi
 ])

configure.ac

@@ -59,8 +59,8 @@ if ! test -f "$srcdir/lib/asn1/der-protos.h" ||
     AC_KRB_PERL_MOD(JSON)
 fi
 
-dnl AC_KRB_PROG_YACC
+AC_KRB_PROG_YACC
-AC_PROG_YACC
+dnl AC_PROG_YACC
 AM_PROG_LEX
 AS_IF([$LEX --nounput -V > /dev/null 2>&1 && test $? -eq 0],
       [AC_SUBST([FLEXNOUNPUTARGS], ["--nounput"])],