[clang] [llvm] [DropUnnecessaryAssumes] Add pass for dropping assumes (PR #159403)

[Hassnaa Hamdi via cfe-commits]

hassnaaHamdi wrote:

@nikic 
I have been working on enabling speculative devirtualization out of LTO.
Also unfortunately the inlining is important here to run before the devirtualization because the constructors get inlined and that make the mission easier for other passes that optimise the dead GVs and then finally the devirtualization pass runs after that.

I have looked at the pass, and I see that it avoids `type_test` intrinsic, I think it should also avoid `public_type_test` ? I think this could be just the solution here.

https://github.com/llvm/llvm-project/pull/159403