Only profiling when it's enabled. (#121404)
Summary:
The profiling, even when disabled, takes up about 1.5% cpu for a model I'm looking into.
This patch just splits into with/without profile runs.
The potential downside is that now the script can't enable profiling in itself. It doesn't seem to be used anywhere. If that's a crusial usecase, we can do something about it but ideally we wouldn't.
Test Plan:
Link with profiles:
https://fburl.com/scuba/strobelight_services/ihxsl7pj
```
buck2 run fbcode//caffe2/test/cpp/jit:jit
```
Reviewed By: zhxchen17
Differential Revision: D54066589
Pull Request resolved: https://github.com/pytorch/pytorch/pull/121404
Approved by: https://github.com/zhxchen17
