[llvm] [SLP] Use static_assert() rather than assert() where possible (PR #180867)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 commented:

This is more of an ADT change than anything else (added reviewers). This might make sense to split from the SLP change.

https://github.com/llvm/llvm-project/pull/180867