MDEV-11212 - Clean-up MariaDB atomic operations
MDEV-11212 - Clean-up MariaDB atomic operations

Removed gcc transparent union hack that was supposed to suppress gcc warnings.
If there're warnings still it is to be fixed differently and the fix should
be platform independent.

natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2