HPCC-9153 UNIMPLEMENTED on OSX

A couple of places in jutil.cpp throw an UNIMPLEMENTED on OSX for no good
reason.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #4253 from richardkchapman/OSX-unimplemented

HPCC-9153 UNIMPLEMENTED on OSX

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>