Relates to https://github.com/llvm/llvm-project/issues/54337
This is just a comment referencing distutils but even so, we can ditch
the custom which and use the one Python 3.3 added. Which has the .bat
bug fixed:
https://docs.python.org/3.3/library/shutil.html#shutil.which
I tested this on Windows:
```
C:\Users\tcwg>touch foo.bat
C:\Users\tcwg>python
Python 3.11.9 (tags/v3.11.9:de54cf5, Apr 2 2024, 12:24:25) [MSC v.1938 64 bit (ARM64)] on win32 Type "help", "copyright", "credits" or "license" for more information.
>>> import shutil
>>> shutil.which("foo")
'.\\foo.BAT'
```
I just ran the script manually and got reasonable results, I haven't
done a GN build.
3308fc4acd