Add deprecation message for constant buffer branch (#12295)

Summary:
Pull Request resolved: #12295

Add a warning message before deprecation. There are a bunch of PTE files still using this branch: D77626530

Reviewed By: larryliu0820

Differential Revision: D77965467

Author: lucylq

runtime/executor/program.cpp

@@ -219,6 +219,14 @@ Result<executorch_flatbuffer::ExecutionPlan*> get_execution_plan(
   } else {
     // The constant data is stored inside the flatbuffer, so this program does
     // not contain a separate segment for it.
+
+    // NOTE: This branch is deprecated from ExecuTorch 0.7 onwards.
+    // Please regenerate your PTE file to ensure newer ExecuTorch runtimes can support it.
+    // ExecuTorch deprecation policy: https://docs.pytorch.org/executorch/stable/api-life-cycle.html#deprecation-policy.
+    // For support, contact the PyTorch Edge team or make an issue in: https://github.com/pytorch/executorch/issues.
+    ET_LOG(
+        Error,
+        "!!DEPRECATED!! This branch is deprecated from ExecuTorch 0.7; re-export this PTE file to ensure support on newer runtimes.");
     return Program(
         loader,
         segment_base_offset,