Fix JSONDecodeError when using compiler modules (#25624)

When using modules for compiler (and/or external package), if a
package's `setup_[dependent_]build_environment` sets `PYTHONHOME`, it
can influence the python subprocess executed to gather module
information.

The error seen was:

```
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)
```

But the actual hidden error happened in the `python -c 'import
json...'` subprocess, which made it return an empty string as json:

```
ModuleNotFoundError: No module named 'encodings'
```

This fix uses `python -E` to ignore `PYTHONHOME` and
`PYTHONPATH`. Should be safe here because the python subprocess code
only use packages built-in python.

The python subprocess in `environment.py` was also patched to be safe
and consistent.

0 files changed, 0 insertions, 0 deletions