[llvm] [LangRef/DataLayout] Spell out requirements for alignment values (PR #104705)

[Nikita Popov via llvm-commits]

nikic wrote:

> For 'a', the implementation currently allows 0 for both `<abi>` and `<pref>` components. The added wording prohibits specifying zero for `<pref>` with the same justification as above. Zero `<abi>` is used in tests, and the example at the end of the section suggests that this is valid, so that's left unchanged.

Looks like the data layouts emitted by clang even use `a:0`, so yeah, it doesn't look like we can change that part without more effort than it is worth...

https://github.com/llvm/llvm-project/pull/104705