Emit LLVM bytecode assembly

Signed-off-by: Pekka Enberg <penberg@iki.fi>
Codegen: Return an empty list of instructions

Return an empty list of instructions instead of 'undefined'. Taylor now
prints out LLVM bytecode assembly (with no instructions, of course).

Signed-off-by: Pekka Enberg <penberg@iki.fi>