[llvm] Add DILabel functions for LLVM-C (PR #112840)

[via llvm-commits]

tf2spi wrote:

@echristo Hello! I'm a new contributor in LLVM. After reading the [LLVM Contributing Guide](https://llvm.org/docs/Contributing.html#how-to-submit-a-patch), it suggested to ping you when the code is ready to review. Any time that's convenient for you to review this I would greatly appreciate.

https://github.com/llvm/llvm-project/pull/112840