[clang] [Inliner] Improve propagation of return attributes. (PR #67756)

[Nikita Popov via cfe-commits]

nikic wrote:

For the clang tests you've split, the `.c` versions still have `defined(__cplusplus)` checks, which doesn't make much sense.

Though I think we might be better off passing `-no-enable-noundef-analysis` to these tests, as noundef is really not what they want to test.

https://github.com/llvm/llvm-project/pull/67756