HPCC-10070 Update needed to eclcc regression test instructions in sourcedoc.xml

Instructions in sourcedoc.xml state -r syntax for regress.sh that is no
longer supported.

Signed-off-by: jamienoss <james.noss@lexisnexis.com>
Merge pull request #4863 from jamienoss/issue10070-sourcedoc.xml-regress.sh-syntax

HPCC-10070 Change to eclcc regression test instructions in sourcedoc.xml

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>