HPCC-11394 Support latest version of Rcpp

Previous fix gave some issues on Centos builds

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #6047 from richardkchapman/rembed-fix2

HPCC-11394 Support latest version of Rcpp

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>