[clang] [llvm] [LLVM][Clang] Add and enable strict mode for `getTrailingObjects` (PR #144930)

[Erich Keane via cfe-commits]

erichkeane wrote:

> Just to be precise, it's not the number of items but the number of trailing types. I half expected the comment to make it a different function. I'll do that

Ah right, I was using 'items' to mean 'types' too, so we were clear there :)  Sorry for my lack of precision.

https://github.com/llvm/llvm-project/pull/144930