[DirectX] Legalize Lifetime markers

[farzonl]

Problem

We noticed many cases of DXC where we don't emit lifetime markers where clan-dxc does emit them. We were hesitant to allow these to pass on through because we weren't sure if they were correct.

Solution

We have since determined that its likely that DXC is missing lifetime markers that it should be adding and so its likely safe to make a change in llvm/lib/Target/DirectX/DXILOpLowering.cpp to let lifetime intrinsics pass on through.