handle failures to find a user home directory

In certain environments (notably, the [bazel sandbox](https://bazel.build/docs/sandboxing) on windows), it is possible for `pathlib.Path('~').expanduser()` to fail to find the user home directory and [raise a `RuntimeError`](https://docs.python.org/3/library/pathlib.html#pathlib.Path.expanduser). This causes `distutils` (and ultimately, `setuptools`) to fail.

With this patch, we catch and handle the exception by logging a warning and continuing without a user's config file.

motivated by bazel-contrib/rules_python#1067

Author: cj81499

distutils/dist.py

@@ -354,7 +354,12 @@ def _gen_paths(self):
         prefix = '.' * (os.name == 'posix')
         filename = prefix + 'pydistutils.cfg'
         if self.want_user_cfg:
-            yield pathlib.Path('~').expanduser() / filename
+            try:
+                user_home = pathlib.Path('~').expanduser()
+            except RuntimeError:
+                self.announce("Failed to locate user home directory. Skipping user config.", logging.WARNING)
+            else:
+                yield user_home / filename
 
         # All platforms support local setup.cfg
         yield pathlib.Path('setup.cfg')