HPCC-9226 Fix build break on Centos

Seems execvpe is not always available.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #4334 from richardkchapman/build-break-centos

HPCC-9226 Fix build break on Centos

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>
Merge remote-tracking branch 'origin/candidate-3.10.8' into candidate-3.10.x

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge remote-tracking branch 'origin/candidate-3.10.x' into candidate-4.0.0

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Community Edition 4.0.0-rc6 Release Candidate 6

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