[llvm] [IR] Composable and Extensible Memory Cache Control Hints (PR #181612)

[Antonio Frighetto via llvm-commits]

https://github.com/antoniofrighetto commented:

> * Registration of mem.cache_hint in FixedMetadataKinds (MD ID 48)

Nit: s/48/50/ (meanwhile other metadata have landed...)

https://github.com/llvm/llvm-project/pull/181612