HPCC-10846 Allow #option ('saveCppTempFiles') to preserve C++ files.

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #5438 from ghalliday/issue10846

HPCC-10846 Allow #option ('saveCppTempFiles') to preserve C++ files.

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>