[inductor] Allow backend compiler to skip (#111153)
Summary:
Sometimes the backend compiler can encounter a transient failure (in
our case, a remote build service infrequently hits a hiccup). We'd rather run
eager than fail the training job.
Test Plan:
Inject an exception in the RE path and run:
```
buck2 run @//mode/{opt,inplace} //caffe2/test/inductor:smoke
```
Differential Revision: D50234516
Pull Request resolved: https://github.com/pytorch/pytorch/pull/111153
Approved by: https://github.com/ezyang, https://github.com/jansel
