[llvm] [IR] Add nowrap flags for trunc instruction (PR #85592)

[via llvm-commits]

elhewaty wrote:

> Another place to update is SCEVExpander, which backs up poison-generating flags. Needs an adjustment to handle these on trunc now. (Don't think this needs a test, it's pretty tricky to do that.)

before modifying the SCEVExpander, are these places legal to modify [here](https://github.com/llvm-mirror/llvm/blob/master/lib/Analysis/ScalarEvolution.cpp#L4434), should we add a class like [this](https://github.com/llvm-mirror/llvm/blob/master/lib/Analysis/ScalarEvolution.cpp#L4470), should we modift [this](https://llvm.org/doxygen/ScalarEvolution_8cpp_source.html#l02382) to


https://github.com/llvm/llvm-project/pull/85592