Have setup.py unset HOME when running buck2 (#3467)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/3467

setup.py is sometimes run as root in docker containers. buck2 doesn't
allow running as root unless $HOME is owned by root or does not exist.
So temporarily undefine it while configuring cmake, which runs buck2 to
get some source lists.

Also, the buck2 daemon can sometimes get stuck on the CI workers. Try
killing it before starting the build, ignoring any failures.

imported-using-ghimport

Test Plan: Imported from OSS

Reviewed By: larryliu0820

Differential Revision: D56857494

Pulled By: dbort

fbshipit-source-id: fda4516400ef5a181d76a28be36ca20e02a432ad