get compiler tests to build

This version of the compiler has working proofs on the compiler-proofs
branch (modulo minor changes in the implementation for modules), and now
runs and passes its tests here on refactor. The proofs won't work here
yet because the proofs don't know about modules or about the refactor.
add sem_heap to .gitignore

although maybe we should standardise on the heap names and only have to
ignore one pattern...