Provide tests for intrinsics/builtins support

[PhilippvK]

No description provided.

[thomasgoodfellow]

This task will provide a small set of test cases for a couple of specimen ISAs (NN, S4E), basically to confirm that the same functionality that was present in S4Ephase1 has been reproduced. An additional task will cover the wider scope of generating intrinsics for arbitrary extensions (similarly testing is needed for the support for such instructions, e.g. with all possible datatypes, number of arguments, etc)