Back out "Revert export_for_training migration in llm/export/builder.py" (#6180)

Summary:
Pull Request resolved: #6180

Revert back change since we have fixed the issue in pytorch/pytorch#137540  with  D64080561.

Reviewed By: dvorjackz

Differential Revision: D64260221

fbshipit-source-id: 500af6faf02f160b67c4c010962a9b3a5312f3a7

Author: yushangdi

extension/llm/export/builder.py

@@ -29,10 +29,10 @@
 
 from executorch.extension.export_util.utils import export_to_edge, save_pte_program
 from executorch.extension.llm.tokenizer.utils import get_tokenizer
-from torch._export import capture_pre_autograd_graph
 from torch.ao.quantization.quantize_pt2e import convert_pt2e, prepare_pt2e
 from torch.ao.quantization.quantizer import Quantizer
 from torch.ao.quantization.quantizer.composable_quantizer import ComposableQuantizer
+from torch.export import export_for_training
 from torch.nn.attention import SDPBackend
 
 FORMAT = "[%(levelname)s %(asctime)s %(filename)s:%(lineno)s] %(message)s"
@@ -193,12 +193,12 @@ def capture_pre_autograd_graph(self) -> "LLMEdgeManager":
                     strict=True,
                 ).module()
             else:
-                self.pre_autograd_graph_module = capture_pre_autograd_graph(
+                self.pre_autograd_graph_module = export_for_training(
                     self.model,
                     self.example_inputs,
                     kwargs=self.example_kwarg_inputs,
                     dynamic_shapes=dynamic_shape,
-                )
+                ).module()
 
         return self