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

[via llvm-commits]

tf2spi wrote:

I also noticed there's an [LLVM-C DebugInfo](https://github.com/llvm/llvm-project/blob/main/llvm/tools/llvm-c-test/debuginfo.c) test. Do tests for new features normally get added in the same PR or in a separate one? 

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