Fix C++ -Werror regressions in llama runner (#19326)

[psiddh]

Summary:

Fixes 3 -Werror diagnostics that broke the qualcomm llama runner build on
cfg:android-arm64-clang19-no-san and disabled the following test infra
targets:

• xplat/executorch/examples/qualcomm/oss_scripts/llama:runner_lib
• xplat/executorch/examples/qualcomm/oss_scripts/llama:runner_lib_static
• xplat/executorch/examples/qualcomm/oss_scripts/llama:qnn_llama_runner
• xplat/executorch/examples/qualcomm/oss_scripts/llama:qnn_llama_runner_static

Three diagnostics fixed:

1. -Wreorder-ctor in runner.cpp: attention_sink_rope_module_ is
   declared as the 2nd field of Runner<T> (right after module_) but the
   constructor initializer list appended it last, after tokenizer_. Moved
   it to the correct position in the init list to match declaration order.
   Recent regression introduced in the attention-sink diff (Qualcomm AI Engine Direct - Support attention sink for long context usecase #16574).

2. -Woverloaded-virtual in lhd_token_generator.h and
   multimodal_lhd_token_generator.h: the derived classes define a
   prepare_io(std::vector<uint64_t>, std::vector<int32_t>) overload that
   hides the base class virtual prepare_io(uint64_t, int64_t). Added a
   using TokenGenerator<T>::prepare_io; (and equivalent for the
   multimodal hierarchy) declaration so the base virtual stays in scope and
   the warning is silenced without changing behavior. Latent bug surfaced
   by the clang19 toolchain bump.

3. -Wdelete-non-abstract-non-virtual-dtor in prompt_processor.h:
   PromptProcessor<T> has virtual member functions but no virtual
   destructor, so deleting via std::unique_ptr<PromptProcessor<T>> in
   Runner was undefined behavior under strict warnings. Added
   virtual ~PromptProcessor() = default; mirroring the pattern already
   used in TokenGenerator (token_generator.h). Also transitively
   fixes MultimodalPromptProcessor<T>.

Reviewed By: rascani

Differential Revision: D103991803

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/19326

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❌ 1 New Failure, 1 Cancelled Job, 6 Pending, 3 Unrelated Failures

As of commit 2f66064 with merge base 1debeb6 ():

NEW FAILURE - The following job has failed:

• pull / android / run-emulator (gh)
  The process '/usr/bin/sh' failed with exit code 1

CANCELLED JOB - The following job was cancelled. Please retry:

• pull / unittest-editable / macos / macos-job (gh)

BROKEN TRUNK - The following jobs failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / unittest / macos / macos-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• Test CoreML Backend / test-coreml / test-backend-macos (coreml, models) / macos-job (gh) (trunk failure)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1
• Test CoreML Backend / test-coreml / test-backend-macos (coreml, operators) / macos-job (gh) (trunk failure)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1

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[meta-codesync]

@psiddh has exported this pull request. If you are a Meta employee, you can view the originating Diff in D103991803.

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[Copilot]

Pull request overview

This PR addresses clang19 -Werror build regressions in the Qualcomm llama runner by fixing constructor member initialization order, correcting virtual function hiding warnings, and ensuring safe polymorphic deletion via a virtual destructor.

Changes:

• Reordered Runner<T> constructor initializer list to match member declaration order (-Wreorder-ctor).
• Added using ...::prepare_io declarations in LHD token generator subclasses to avoid hiding base virtuals (-Woverloaded-virtual).
• Added a virtual destructor to PromptProcessor<T> to avoid UB when deleting through base pointers (-Wdelete-non-abstract-non-virtual-dtor).

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
examples/qualcomm/oss_scripts/llama/runner/runner.cpp	Fixes member initializer order to satisfy -Wreorder-ctor.
examples/qualcomm/oss_scripts/llama/runner/prompt_processor.h	Adds virtual destructor to make polymorphic deletion well-defined.
examples/qualcomm/oss_scripts/llama/runner/lhd_token_generator.h	Brings base prepare_io into scope to avoid -Woverloaded-virtual.
examples/qualcomm/oss_scripts/llama/runner/multimodal_runner/multimodal_lhd_token_generator.h	Attempts to bring base prepare_io into scope for multimodal LHD (but see review comment re: private access).

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