[llvm] [unittests] Add missing includes (PR #65681)

[Paul T Robinson via llvm-commits]

https://github.com/pogo59 requested changes to this pull request.

I see only two places that use DoAll in llvm/unittests, and the other one has the `using` clause, so it makes sense to have it here.

TextStubHelpers.h looks like it doesn't use SmallString, so that include should go in the files where it's actually needed.

https://github.com/llvm/llvm-project/pull/65681