[llvm] Check hasOptSize() in shouldOptimizeForSize() (PR #112626)

[Paul Walker via llvm-commits]

https://github.com/paulwalker-arm approved this pull request.

>From an interface point of view this means all BBs passed into the various shouldOptimizeForSize functions must now be attached to a function.  I'm not aware of that being an issue so this looks like a nice refactor to me but please give other reviewers a day to chip in just in case they have a concern over the new requirement.

https://github.com/llvm/llvm-project/pull/112626