signal (6) if numba is imported after julia

If numba is imported after a PyJulia session is started, the process fails and exits. This does not occur if numba is imported first. Example:

```
Python 3.7.3 (default, Mar 27 2019, 09:23:15)
[Clang 10.0.1 (clang-1001.0.46.3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from julia import Main
>>> import numba
Assertion failed: (PassInf && "Expected all immutable passes to be initialized"), function addImmutablePass, file /Users/buildbot/miniconda3/conda-bld/llvmdev_1556270736866/work/lib/IR/LegacyPassManager.cpp, line 849.

signal (6): Abort trap: 6
in expression starting at no file:0
__pthread_kill at /usr/lib/system/libsystem_kernel.dylib (unknown line)
Allocations: 9604414 (Pool: 9602251; Big: 2163); GC: 20
[1] 93402 abort python3
```

I'm using julia `v1.1.1`, PyJulia `v0.4.1`, and numba `v0.44.1`.