Add regression test to track main function number

[IlmariReissumies]

The compiler assumes that the main function is the first function after the various stubs introduced in data_to_word; at the time of writing, this is function 62. This number isn't specified anywhere, but is rather calculated.

The Pancake compiler needs to somehow know what this number is going to be, which is currently done by hard-coding it in crep_to_loop as follows

Definition first_name_def:
  first_name = 62:num
End

I think this hardcoding is not terrible: the alternative would be to have the pancake compiler depend on data_to_word. But it does create hard-to-trace errors whenever stubs are added or removed, causing the number to be out of synch. The end-to-end proofs for Pancake, once they exist, should break when this happens. But until they do, it would be nice to have some way of keeping them synched.

This issue is to create a regression test which fails if the number of stubs and first_name fails to line up.