[llvm] [NFC] Pack MDNodeKeyImpl<DILocation> from 40 to 32 bytes (PR #143891)

[Orlando Cazalet-Hyams via llvm-commits]

OCHyams wrote:

32->24 without KeyInstructions support.

I don't think this massively affects anything, so can discard if it's just churn. Feels like it couldn't hurt though? Noticed while prodding around in the area.

https://github.com/llvm/llvm-project/pull/143891