Builder creation

[mrexodia]

    types = module.context.types
    i64 = types.i64
    lift2_ty = types.function(i64, [i64, i64])
    lift2 = module.add_function("lift2", lift2_ty)
    with lift2.create_builder() as ir:
        ir.ret(i64.constant(0))

Raises:

Traceback (most recent call last):
  File "/Users/duncan/Projects/striga/brighten.py", line 16, in <module>
    with lift2.create_builder() as ir:
         ~~~~~~~~~~~~~~~~~~~~^^
llvm.LLVMAssertionError: create_builder requires an instruction value