work around diagnostic changes in Bison 3.6

Bison <3.6 used to complain about "$undefined", while Bison >=3.6 now
write "invalid token".

* tests/core/parseaut.test, tests/core/parseerr.test,
tests/core/sugar.test: Adjust expected diagnostics to match Bison pre
and post 3.6.

tests/core/parseaut.test

@@ -1,6 +1,6 @@
 #!/bin/sh
 # -*- coding: utf-8 -*-
-# Copyright (C) 2014-2018 Laboratoire de Recherche et Développement de
+# Copyright (C) 2014-2018, 2020 Laboratoire de Recherche et Développement de
 # l'Epita (LRDE).
 #
 # This file is part of Spot, a model checking library.
@@ -31,7 +31,9 @@ expecterr()
    # If autfilt is compiled statically, the '.../lt-' parse of
    # its name is not stripped, and the error message show the
    # full path.
-   sed 's:^\.\./\.\./bin/::' $1.err-t >$1.err
+   # Also work around differences between Bison >=3.6 (invalid token)
+   # end Bison <3.6 ($undefined).
+   sed 's:^\.\./\.\./bin/::;s/[$]undefined/invalid token/' $1.err-t >$1.err
    cat $1.err
    diff $1.err $1.exp
 }
@@ -1226,21 +1228,22 @@ garbage
 EOF
 
 se='syntax error, unexpected'  # this is just to keep lines short
+undefined='invalid token'
 expecterr input <<EOF
 input:8.11: $se identifier, expecting integer or '}'
 input:8.10-12: ignoring this invalid acceptance set
 input:11.2: $se identifier
 input:11.1-3: ignoring this invalid label
 input:21.5-7: $se string, expecting integer
-input:25.1: $se \$undefined
+input:25.1: $se $undefined
 input:32.1-5: $se header name, expecting --END-- or State:
 input:28.1-8: initial state 0 has no definition
 input:25.1-12: leading garbage was ignored
 input:37.1: $se 't'
-input:43.1: $se \$undefined
-input:56.1: $se \$undefined, expecting State: or end of DSTAR automaton
+input:43.1: $se $undefined
+input:56.1: $se $undefined, expecting State: or end of DSTAR automaton
 input:37.1-39.21: leading garbage was ignored
-input:81.1: $se \$undefined
+input:81.1: $se $undefined
 autfilt: failed to read automaton from input
 EOF
 

tests/core/parseerr.test

@@ -1,6 +1,6 @@
 #! /bin/sh
 # -*- coding: utf-8 -*-
-# Copyright (C) 2009, 2010, 2011, 2013, 2014, 2015, 2016 Laboratoire
+# Copyright (C) 2009-2016, 2020 Laboratoire
 # de Recherche et Développement de l'Epita (LRDE).
 # Copyright (C) 2003, 2004 Laboratoire d'Informatique de Paris 6 (LIP6),
 # département Systèmes Répartis Coopératifs (SRC), Université Pierre
@@ -36,7 +36,7 @@ a - b
 {a[*9999999999]}
 EOF
 
-run 1 ../ltl2text input >output
+run 1 ../ltl2text input | sed 's/[$]undefined/invalid token/g' > output
 
 sed 's/$$//' >expected<<\EOF
 >>> $
@@ -53,7 +53,7 @@ ignoring trailing garbage
 
 >>> /2/3/4/5 a + b /6/7/8/
     ^
-syntax error, unexpected $undefined
+syntax error, unexpected invalid token
 
 >>> /2/3/4/5 a + b /6/7/8/
     ^^^^^^^^^^^^^^^^^^^^^^
@@ -61,7 +61,7 @@ ignoring trailing garbage
 
 >>> a - b
       ^
-syntax error, unexpected $undefined
+syntax error, unexpected invalid token
 
 >>> a - b
       ^^^

tests/core/sugar.test

@@ -1,7 +1,7 @@
 #! /bin/sh
 # -*- coding: utf-8 -*-
-# Copyright (C) 2018, 2019 Laboratoire de Recherche et Développement
-# de l'Epita (LRDE).
+# Copyright (C) 2018-2020 Laboratoire de Recherche et Développement de
+# l'Epita (LRDE).
 #
 # This file is part of Spot, a model checking library.
 #
@@ -135,11 +135,12 @@ EOF
 num="number for square bracket operator"
 numoreof="$num or end of formula"
 sep="separator for square bracket operator"
-undefined='$undefined'
+undefined='invalid token'
 closingbkt='square bracket operator, expecting closing bracket'
 eclosingbkt='expecting closing bracket or closing !]'
 
 ltlfilt -F err.in 2>err && exit 1
+sed 's/[$]undefined/invalid token/' err >err2
 cat >expect2 <<EOF
 ltlfilt:err.in:1: parse error:
 >>> F[
@@ -329,4 +330,4 @@ syntax error, unexpected closing brace
 missing right operand for "SVA delay operator"
 
 EOF
-diff -u err expect2
+diff -u err2 expect2