HPCC-11846 Fix various clang warnings

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #6197 from ghalliday/issue11846

HPCC-11846 Fix various clang warnings

Reviewed-By: Jake Smith <jake.smith@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>