MDEV-24393 InnoDB disregards --skip-external-locking

On POSIX systems, InnoDB would unconditionally acquire advisory locks
on the files that it opens. On Linux, this would be observable by
a large number of entries in /proc/locks.

Other storage engines would only acquire advisory locks on files
based on the Boolean configuration parameter external_locking.

Let InnoDB do the same.

NOTE: The --skip-external-locking is activated by default. To have
InnoDB acquire advisory locks, --external-locking must be specified.

Reviewed by: Sergei Golubchik

include/my_sys.h

 /* Copyright (c) 2000, 2013, Oracle and/or its affiliates.
-   Copyright (c) 2010, 2017, MariaDB Corporation.
+   Copyright (c) 2010, 2021, MariaDB Corporation.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -279,7 +279,8 @@ extern int my_umask_dir,
 extern my_bool my_use_symdir;
 
 extern ulong	my_default_record_cache_size;
-extern my_bool  my_disable_locking, my_disable_async_io,
+extern MYSQL_PLUGIN_IMPORT my_bool my_disable_locking;
+extern my_bool  my_disable_async_io,
                 my_disable_flush_key_blocks, my_disable_symlinks;
 extern my_bool my_disable_sync, my_disable_copystat_in_redel;
 extern char	wild_many,wild_one,wild_prefix;

storage/innobase/os/os0file.cc

@@ -1122,6 +1122,10 @@ os_file_lock(
 	int		fd,
 	const char*	name)
 {
+	if (my_disable_locking) {
+		return 0;
+	}
+
 	struct flock lk;
 
 	lk.l_type = F_WRLCK;