[llvm] [ValueTracking] Handle assume( trunc x to i1) (PR #118406)

[Andreas Jonson via llvm-commits]

andjo403 wrote:

Have rebased and fixed the comments so this is ready for a new review.
have excluded the fold `not (trunc to i1)`  to avoid  the "ephemeral value" issue that was present before in this PR. 

https://github.com/llvm/llvm-project/pull/118406