When nopython=True, Dynamo can't allow graph breaks. (#90970)
I count the number of sub-graphs (for tiny-GPT2 in huggingface) by
```
class GraphCaptureCompiler:
def __init__(self):
self.captured_graphs = []
def compile(self, gm, example_inputs):
self.captured_graphs.append(gm)
return gm
compiler = GraphCaptureCompiler()
torch._dynamo.optimize(compiler, nopython=True)(Wrapper(fn))(*args)
```
Although `len(compiler.captured_graphs)` is 2, no error was thrown during the compilation. This observation conflicts with `nopython=True`. After some digging, I found a check is missed before making graph break. This PR adds it.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/90970
Approved by: https://github.com/ezyang, https://github.com/jansel
