Bug#51631 general-log flag doesn't accept "on" as a value in

          the my.cnf, works as command
      
Different parsing mechanisms are used for command line/my.cnf 
options  and the SQL commands.  The former only accepted
numeric arguments, and regarded all numbers different from 0 
as 'true'.  Any other argument was parsed as 'false' .
      
This patch adds the words 'true' and 'on' as valid truth
values for boolean option arguments.
      
A test case is not provided, as the fix is simple and
does not warrant a separate test file (no existing
suitable test file was found)

(backported from mysql-trunk)

mysys/my_getopt.c

@@ -602,6 +602,24 @@ static char *check_struct_option(char *cur_arg, char *key_name)
   }
 }
 
+/**
+   Parse a boolean command line argument
+
+   "ON", "TRUE" and "1" will return true,
+   other values will return false.
+
+   @param[in] argument The value argument
+   @return boolean value
+*/
+static my_bool get_bool_argument(const char *argument)
+{
+  if (!my_strcasecmp(&my_charset_latin1, argument, "true") ||
+      !my_strcasecmp(&my_charset_latin1, argument, "on"))
+    return 1;
+  else
+    return (my_bool) atoi(argument);
+}
+
 /*
   function: setval
 
@@ -629,7 +647,7 @@ static int setval(const struct my_option *opts, void *value, char *argument,
 
     switch ((opts->var_type & GET_TYPE_MASK)) {
     case GET_BOOL: /* If argument differs from 0, enable option, else disable */
-      *((my_bool*) value)= (my_bool) atoi(argument) != 0;
+      *((my_bool*) value)= get_bool_argument(argument);
       break;
     case GET_INT:
       *((int*) value)= (int) getopt_ll(argument, opts, &err);