[clang] [llvm] [IR] Make dead_on_return attribute optionally sized (PR #171712)

[Aiden Grossman via cfe-commits]

boomanaiden154 wrote:

@antoniofrighetto @nikic  I think this is ready for another round of review when people have a chance. I've posted the DSE changes in https://github.com/llvm/llvm-project/pull/173694.

https://github.com/llvm/llvm-project/pull/171712