[PyCDE] No module named "numpy"/"jinja2" during compilation

Nobody has claimed this yet.

When I try to compile PyCDE (cannot install cause using Apple M1), I have the following error (in many places):

```
Traceback (most recent call last):
File "/Users/vmois/Projects/circt/frontends/PyCDE/test/test_xrt.py", line 20, in
import pycde
File "/Users/vmois/Projects/circt/frontends/PyCDE/build/cmake_build/tools/circt/python_packages/pycde/pycde/__init__.py", line 22, in
from .module import (generator, modparams, Module)
File "/Users/vmois/Projects/circt/frontends/PyCDE/build/cmake_build/tools/circt/python_packages/pycde/pycde/module.py", line 11, in
from .signals import ClockSignal, Signal, _FromCirctValue
File "/Users/vmois/Projects/circt/frontends/PyCDE/build/cmake_build/tools/circt/python_packages/pycde/pycde/signals.py", line 18, in
import numpy as np
ModuleNotFoundError: No module named 'numpy'
```
After checking required packages, I can see that numpy is present:

https://github.com/llvm/circt/blob/c9c359159ad977892e13865e83c8cd0951b21e74/frontends/PyCDE/pyproject.toml#L2-L17

I have installed numpy manually (`pip install numpy`), but now a different package is missing - `jinja2`. After manually installing `jinja2`, I managed to build pycde and it works! But, strangely, packages are not found while specified in `required`. Any ideas why it can be?

I am using conda env and Python 3.8.

Start with frontends/PyCDE/pyproject.toml and the import path shown in the traceback, then reproduce test/test_xrt.py in a conda environment using Python 3.8. Check why the declared numpy and jinja2 dependencies are unavailable during the PyCDE build; done means a supported build environment resolves them without manual installation.

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