report: use %empty to denote empty rules

* src/gram.c (rule_rhs_print): Use %empty for empty rules.
* tests/conflicts.at, tests/regression.at, tests/sets.at: Adjust.

tests/conflicts.at

@@ -1299,13 +1299,13 @@ AT_CHECK([[cat input.output]], 0,
     2 resolved_conflict: 'a' unreachable1
 
     4 unreachable1: 'a' unreachable2
-    5             | /* empty */
+    5             | %empty
 
-    6 unreachable2: /* empty */
-    7             | /* empty */
+    6 unreachable2: %empty
+    7             | %empty
 
     9 reported_conflicts: 'a'
-   10                   | /* empty */
+   10                   | %empty
 
 
 State 4 conflicts: 1 shift/reduce
@@ -1319,17 +1319,17 @@ Grammar
     1 start: resolved_conflict 'a' reported_conflicts 'a'
 
     2 resolved_conflict: 'a' unreachable1
-    3                  | /* empty */
+    3                  | %empty
 
     4 unreachable1: 'a' unreachable2
-    5             | /* empty */
+    5             | %empty
 
-    6 unreachable2: /* empty */
-    7             | /* empty */
+    6 unreachable2: %empty
+    7             | %empty
 
     8 reported_conflicts: 'a'
     9                   | 'a'
-   10                   | /* empty */
+   10                   | %empty
 
 
 Terminals, with rules where they appear

tests/regression.at

@@ -263,11 +263,11 @@ AT_CHECK([cat input.output], [],
 
     0 $accept: expr $end
 
-    1 $@1: /* empty */
+    1 $@1: %empty
 
     2 expr: 'a' $@1 'b'
 
-    3 $@2: /* empty */
+    3 $@2: %empty
 
     4 expr: $@2 'c'
 
@@ -573,7 +573,7 @@ AT_CHECK([cat input.output], 0,
     2 CONST_DEC_LIST: CONST_DEC
     3               | CONST_DEC_LIST CONST_DEC
 
-    4 $@1: /* empty */
+    4 $@1: %empty
 
     5 CONST_DEC: $@1 undef_id_tok '=' const_id_tok ';'
 

tests/sets.at

@@ -86,7 +86,7 @@ AT_CHECK([[cat sets]], [],
       0  e $end
   e derives
       1  'e'
-      2  /* empty */
+      2  %empty
 NULLABLE
   $accept: no
   e: yes
@@ -100,10 +100,10 @@ FDERIVES
   $accept derives
       0  e $end
       1  'e'
-      2  /* empty */
+      2  %empty
   e derives
       1  'e'
-      2  /* empty */
+      2  %empty
 ]])
 
 AT_CLEANUP