[llvm] [ADT] Fix alignment check in unique_function constructor (PR #99403)

[Dmitry Yanovsky via llvm-commits]

kerambyte wrote:

Sounds good, I've added a test that checks the captured pointer lies within the `unique_function` object itself. Documented that we're making a couple assumptions about its implementation as well.

I came across it accidentally in the debugger while working on a unit-test for that PR - https://github.com/llvm/llvm-project/pull/98747



https://github.com/llvm/llvm-project/pull/99403