[llvm] Add Dead Block Elimination to NVVMReflect (PR #144171)

[Yonah Goldberg via llvm-commits]

YonahGoldberg wrote:

You said it yourself that running the existing DCE pass in O0 isn't optimal because that's not what the user wants. The code I wrote only eliminates blocks that become dead as a result from folding reflect calls because it's necessary for valid code. All other dead blocks are left alone.

https://github.com/llvm/llvm-project/pull/144171