MDEV-31989 Cleanup Lex_ident_fs::check_body()

- Changing the data type of the global variable any_db from
  LEX_CSTRING to Lex_ident_db

- Removing the dependency on system_charset_info from
  Lex_ident_fs::check_body(), using my_charset_utf8mb3_general_ci directly,
  because system_charset_info is initialized much later than any_db.
  system_charset_info cannot be changed dynamically any way.

- Removing the unsed old code from Lex_ident_fs::check_body().
  This code was last used in MySQL-4.0 and won't be used in the future.

sql/sql_parse.cc

@@ -126,7 +126,7 @@ static int  show_create_db(THD *thd, LEX *lex);
 static bool alter_routine(THD *thd, LEX *lex);
 static bool drop_routine(THD *thd, LEX *lex);
 
-const LEX_CSTRING any_db= {STRING_WITH_LEN("*any*")};
+const Lex_ident_db any_db(STRING_WITH_LEN("*any*"));
 
 const LEX_CSTRING command_name[257]={
   { STRING_WITH_LEN("Sleep") },           //0

sql/sql_parse.h

@@ -129,7 +129,7 @@ bool check_stack_overrun(THD *thd, long margin, uchar *dummy);
 
 /* Variables */
 
-extern const LEX_CSTRING any_db;
+extern const Lex_ident_db any_db;
 extern uint sql_command_flags[];
 extern uint server_command_flags[];
 extern const LEX_CSTRING command_name[];

sql/table.cc

@@ -5258,27 +5258,17 @@ bool Lex_ident_fs::check_body(const char *name, size_t length,
   size_t char_length= 0;
   const char *end= name + length;
 
-#if defined(USE_MB) && defined(USE_MB_IDENT)
-  bool last_char_is_space= FALSE;
-#else
   if (name[length-1]==' ')
     return 1;
-#endif
 
   for ( ; name != end ; char_length++)
   {
-#if defined(USE_MB) && defined(USE_MB_IDENT)
-    last_char_is_space= my_isspace(system_charset_info, *name);
-    if (system_charset_info->use_mb())
+    int len= my_ismbchar(&my_charset_utf8mb3_general_ci, name, end);
+    if (len)
     {
-      int len=my_ismbchar(system_charset_info, name, end);
-      if (len)
-      {
-        name+= len;
-        continue;
-      }
+      name+= len;
+      continue;
     }
-#endif
     if (disallow_path_chars &&
         (*name == '/' || *name == '\\' || *name == '~' || *name == FN_EXTCHAR))
       return 1;
@@ -5299,11 +5289,7 @@ bool Lex_ident_fs::check_body(const char *name, size_t length,
       return 1;
     name++;
   }
-#if defined(USE_MB) && defined(USE_MB_IDENT)
-  return last_char_is_space || (char_length > NAME_CHAR_LEN);
-#else
-  return FALSE;
-#endif
+  return char_length > NAME_CHAR_LEN;
 }