HPCC-12138 ADD_PLUGIN macro only works if exactly one dependent package

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #6384 from richardkchapman/add-plugin

HPCC-12138 ADD_PLUGIN macro only works if exactly one dependent package

Reviewed-By: Jake Smith <jake.smith@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>
HPCC-0000 WIP

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>