[llvm] [AMDGPU] Add mir serialization for anti-hints (PR #200206)

[Syadus Sefat via llvm-commits]

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mssefat wrote:

Hi Quentin, this PR does not show the MIR serialization changes cleanly. I have created a separate version as a part of the anti-hints stacked PRs. The MIR serialization changes are in this one: https://github.com/llvm/llvm-project/pull/218073

I will close this PR since we have that cleaner version. 

https://github.com/llvm/llvm-project/pull/200206