[inductor] default cache_dir in torch._inductor.codecache should be lazily evaluated (#100824)
`getpass.getuser` may raise exceptions in some circumstances, where users cannot override the default cache dir with env `TORCHINDUCTOR_CACHE_DIR`. Hence the assemble of default cache dir should be lazily evaluated.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/100824
Approved by: https://github.com/ezyang