Format third-party/CMakeLists.txt using cmake-format

[aksharabhardwaj766-commits]

Fixes #10736

Formats third-party/CMakeLists.txt using cmake-format to improve readability and consistency.

Changes:

• Reformatted ExternalProject_Add(...) blocks for flatbuffers and flatcc
• Reflowed set_target_properties(...), set(...) cache variables, and install(...) calls
• No functional changes — formatting only

Note: This is a clean replacement for #17374, which had accumulated unrelated files from merge conflict resolutions.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/18533

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✅ You can merge normally! (2 Unrelated Failures)

As of commit efd725d with merge base d31d4be ():

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 / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• pull / unittest-editable / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.

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[aksharabhardwaj766-commits]

@pytorchbot label "release notes: none"

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[aksharabhardwaj766-commits]

@pytorchbot label release notes: none

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[aksharabhardwaj766-commits]

@pytorchbot label "release notes: none"

[Copilot]

Pull request overview

This PR aims to improve readability/consistency of the project’s third-party build configuration by reformatting third-party/CMakeLists.txt using cmake-format.

Changes:

• Reformats ExternalProject_Add(...) blocks for flatbuffers and flatcc.
• Reflows several set_target_properties(...), cache set(...), and install(...) invocations.

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[aksharabhardwaj766-commits]

Hi @kirklandsign , just a gentle ping — this PR has been approved for about 3 weeks now. Would like to see it land whenever you have a moment. Thank you!