[dynamo] avoid popen.communicate() (#87335)
It seems like when popen.communicate() is used it waits for all the
desendents of popen to close the stdin/stderr. However, if we have
have worker processes running in the child, and the child segfaults,
those processes will stay alive until someone waitpid's the child.
Since those children have open handles to the stdin/stderr pipe,
communicate never returns.
This change just writes the output to temp files and directly calls
wait() on the child, which returns as soon as it dies.
cc @jansel @lezcano @fdrocha
Pull Request resolved: https://github.com/pytorch/pytorch/pull/87335
Approved by: https://github.com/anijain2305, https://github.com/voznesenskym
