build: use bin override if no `python` in PATH

On systems with no "python" in the PATH, e.g. FreeBSD, we should always
create a python symlink in get_bin_override().

PR-URL: https://github.com/nodejs/node/pull/16241


Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>