[clang] [Clang] Automatically enable `-fconvergent-functions` on GPU targets (PR #111076)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

> > -fno-convergent-functions to opt-out if you want to test broken behavior.
> 
> You may legitimately know there are no convergent functions in the TU. We also have the noconvergent source attribute now for this

Think it would be useful to put that on functions in the wrapper headers that definitely aren't convergent? E.g. getting a thread id.

https://github.com/llvm/llvm-project/pull/111076