The maximum innodb key length is 3500 what is hardcoded in
ha_innobase::max_supported_key_length()). The maximum number of innodb indexes
is configured with MAX_INDEXES macro (see also MAX_KEY definition).

The same is currently implemented for blackhole storage engine.

Cherry picked from percona-server 0d90d81c3c507a6b1476246a405504f6e4ef9d4d
Original lp bug 1733049

Reviewed-by: daniel@mariadb.org