HPCC-10071 Allow eclcc regression suite cores to be configured

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #4864 from ghalliday/regresscores

HPCC-10071 Allow eclcc regression suite cores to be configured

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>