RBC fails to call a decorated `@omnisci` function from another

[guilhermeleobas]

The following code fails

@omnisci('T(T)', T=['int8', 'int16', 'int32', 'int64'])
def add(x):
    return x + 1

@omnisci('T(T)', T=['int8', 'int16', 'int32', 'int64'])
def fn(x):
    return add(x)

_, result = omni.sql_execute('select add(i4) from {omnisci.table_name}')
print(list(result))

>       raise TypingError(msg, loc=inst.loc)
E       numba.core.errors.TypingError: Failed in nopython mode pipeline (step: nopython frontend)
E       Untyped global name 'add': Cannot determine Numba type of <class 'rbc.remotejit.Caller'>
E
E       File "rbc/tests/test_omnisci.py", line 728:
E           def fn(x):
E               return add(x)
E               ^

This is a potential blocker for #263