HPCC-10043 Add option to eclcc to restrict compilation to repository

Set --deny=userECL in the eclccserver options to require that all jobs use
only code that is already present on the eclccserver (typically, from an
external repository via eclcc-hook)

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #4853 from richardkchapman/eclcc-require-main

HPCC-10043 Add option to eclcc to restrict compilation to repository

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>