llvm: re-enable PGO on Linux

[cho-m]

Exploring PGO failure since we currently have a large portion of dead code in build.

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• I did not use AI/LLM to create this PR, or I disclosed the tool/model below and reviewed its output; I did not attribute commits to AI and will answer maintainer questions and review comments myself without AI/LLM.

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[cho-m]

May be failing from LLD split. We do build LLD in stage1 but not in later stages. Perhaps that one can be used; otherwise, would need to build LLD in later stages and avoid installing it.