Backporting a cleanup in boolean function from 10.1:

Moving Item_bool_func2 and Item_func_opt_neg from Item_int_func to
Item_bool_func. Now all functions that return is_bool_func()=true
have a common root class Item_bool_func.
This change is needed to fix MDEV-7149 properly.

sql/item_cmpfunc.h

@@ -122,6 +122,8 @@ public:
   Item_bool_func() :Item_int_func() {}
   Item_bool_func(Item *a) :Item_int_func(a) {}
   Item_bool_func(Item *a,Item *b) :Item_int_func(a,b) {}
+  Item_bool_func(Item *a, Item *b, Item *c) :Item_int_func(a, b, c) {}
+  Item_bool_func(List<Item> &list) :Item_int_func(list) { }
   Item_bool_func(THD *thd, Item_bool_func *item) :Item_int_func(thd, item) {}
   bool is_bool_func() { return 1; }
   void fix_length_and_dec() { decimals=0; max_length=1; }
@@ -364,7 +366,7 @@ public:
   virtual bool l_op() const { return 1; }
 };
 
-class Item_bool_func2 :public Item_int_func
+class Item_bool_func2 :public Item_bool_func
 {						/* Bool with 2 string args */
 protected:
   Arg_comparator cmp;
@@ -372,7 +374,7 @@ protected:
 
 public:
   Item_bool_func2(Item *a,Item *b)
-    :Item_int_func(a,b), cmp(tmp_arg, tmp_arg+1),
+    :Item_bool_func(a,b), cmp(tmp_arg, tmp_arg+1),
      abort_on_null(FALSE) { sargable= TRUE; }
   void fix_length_and_dec();
   int set_cmp_func()
@@ -389,14 +391,12 @@ public:
   }
 
   bool is_null() { return MY_TEST(args[0]->is_null() || args[1]->is_null()); }
-  bool is_bool_func() { return 1; }
   CHARSET_INFO *compare_collation() { return cmp.cmp_collation.collation; }
-  uint decimal_precision() const { return 1; }
   void top_level_item() { abort_on_null= TRUE; }
   Arg_comparator *get_comparator() { return &cmp; }
   void cleanup()
   {
-    Item_int_func::cleanup();
+    Item_bool_func::cleanup();
     cmp.cleanup();
   }
 
@@ -646,16 +646,16 @@ public:
 
 */
 
-class Item_func_opt_neg :public Item_int_func
+class Item_func_opt_neg :public Item_bool_func
 {
 public:
   bool negated;     /* <=> the item represents NOT <func> */
   bool pred_level;  /* <=> [NOT] <func> is used on a predicate level */
 public:
   Item_func_opt_neg(Item *a, Item *b, Item *c)
-    :Item_int_func(a, b, c), negated(0), pred_level(0) {}
+    :Item_bool_func(a, b, c), negated(0), pred_level(0) {}
   Item_func_opt_neg(List<Item> &list)
-    :Item_int_func(list), negated(0), pred_level(0) {}
+    :Item_bool_func(list), negated(0), pred_level(0) {}
 public:
   inline void negate() { negated= !negated; }
   inline void top_level_item() { pred_level= 1; }
@@ -686,9 +686,7 @@ public:
   bool fix_fields(THD *, Item **);
   void fix_length_and_dec();
   virtual void print(String *str, enum_query_type query_type);
-  bool is_bool_func() { return 1; }
   CHARSET_INFO *compare_collation() { return cmp_collation.collation; }
-  uint decimal_precision() const { return 1; }
   bool eval_not_null_tables(uchar *opt_arg);
   void fix_after_pullout(st_select_lex *new_parent, Item **ref);
   bool count_sargable_conds(uchar *arg);
@@ -1316,7 +1314,6 @@ public:
   longlong val_int();
   bool fix_fields(THD *, Item **);
   void fix_length_and_dec();
-  uint decimal_precision() const { return 1; }
   void cleanup()
   {
     uint i;
@@ -1337,7 +1334,6 @@ public:
   enum Functype functype() const { return IN_FUNC; }
   const char *func_name() const { return " IN "; }
   bool nulls_in_row();
-  bool is_bool_func() { return 1; }
   CHARSET_INFO *compare_collation() { return cmp_collation.collation; }
   bool eval_not_null_tables(uchar *opt_arg);
   void fix_after_pullout(st_select_lex *new_parent, Item **ref);