HPCC-12565 Add test case for regression suite option

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
It defines a scope that can be used to access the symbols defined with -D.

By default no symbols are imported from outside the file/definition, so you need a way of getting at the root scope in order to have a valid symbol you can select from in the #IFDEFINED.