MDEV-12292 - port "Report timing with more precision" by @dveeden
MDEV-12292 - port "Report timing with more precision" by @dveeden

CLOCKS_PER_SEC not used anymore.
start_timer()/mysql_end_timer() don't make much sense.
Buffer size requirement increased by 1 byte.

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