fix(local_runtime): Search for libs in sys._base_executable when available.

[laramiel]

Search directory for libraries should look in the same directory as sys._base_executable. Since sys._base_executable may be unset, fallback to sys.executable

Found this when trying to build using a venv for tensorstore on Windows:

• Github CI uses nuget to download Python.
• Build sets up a Python venv.

The venv does not include all the lib directories required to link an extension.

Fixes #3172

[rickeylev]

base_executable is missing when building within a venv

But sys._base_executable is suppose to point where the venv's interpreter is, that's its purpose.

I wonder if this problem manifests when the underlying interpreter can't be found, but the venv is otherwise functional? Maybe if the venv has a copy, not symlink to the interpreter? IIRC, windows venvs create copies of python.exe and rely on pyvenv.cfg to point to the correct pythonhome location. Hm, maybe hardlinks on linux/mac result in something similar? ISTR macs also have some funny tricks they pull with the python executable.

In anycase, LGTM

[laramiel]

I thought that it was trying to be the realpath of sys.executable, usually:

https://github.com/python/cpython/blob/main/Modules/getpath.py

But in any event, we may create nested venvs, and sys._base_executable is used to create those nested venvs, so I think that's the appropriate path to use. Also the windows copy thing.