Emitter: guard _RAND_* declarations with ifdef (#1548)

* Emitter: add declare functions ifdef guard

* Emitter: add ifdef initials

* Emitter: add comments, cleanup

* Emitter: changes from code review

- make new methods private
- use .withDefault
- remove empty initial block

Co-authored-by: Schuyler Eldridge <schuyler.eldridge@ibm.com>