[clang] Add Clang attribute to ensure that fields are initialized explicitly (PR #102040)

[Erich Keane via cfe-commits]

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

Marking 'request-changes' not as there are changes needed, but that I have concerns about the implementation that I have to spend some time in a debugger to assuage.

https://github.com/llvm/llvm-project/pull/102040