HPCC-9435 Report a better error if eclcc fails to open stdin

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #4458 from ghalliday/issue9435

HPCC-9435 Report a better error if eclcc fails to open stdin

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>