[llvm] [OpenMP] Add explicit attributes to every function declaration (PR #122399)

[Joseph Huber via llvm-commits]

jhuber6 wrote:

> What is the benefit of doing so?

Trying to remove delta when porting to remove OpenMP because it doesn't accept `pragma omp`. Unfortunately there's some weird codegen differences that doesn't make it work as expected I'm looking into.

https://github.com/llvm/llvm-project/pull/122399