python: set also sys._base_executable as venv uses it

https://github.com/python/cpython/blob/31b61d19abcc63aa28625a31ed75411948fc1e7e/Lib/venv/__init__.py#L130

pkgs/development/interpreters/python/sitecustomize.py

@@ -21,7 +21,7 @@
 if paths:
     functools.reduce(lambda k, p: site.addsitedir(p, k), paths.split(':'), site._init_pathinfo())
 
-# Check whether we are in a venv or virtualenv. 
+# Check whether we are in a venv or virtualenv.
 # For Python 3 we check whether our `base_prefix` is different from our current `prefix`.
 # For Python 2 we check whether the non-standard `real_prefix` is set.
 # https://stackoverflow.com/questions/1871549/determine-if-python-is-running-inside-virtualenv
@@ -33,6 +33,7 @@
 
     if 'PYTHONEXECUTABLE' not in os.environ and executable is not None:
         sys.executable = executable
+        sys._base_executable = executable
     if prefix is not None:
         # Sysconfig does not like it when sys.prefix is set to None
         sys.prefix = sys.exec_prefix = prefix