[llvm] [Offload][OpenMP] Prettify error messages by "demangling" the kernel name (PR #101400)

[Joseph Huber via llvm-commits]

jhuber6 wrote:

> I ran into a similar issue downstream and extended `llvm::demangle` to support these function names itself. Would it make sense to do this upstream too? The format of the unmangled name would be similar to what `prettifyFunctionName` produces except without the mangled name added on the end.

We could possibly make the OpenMP offloading kernel mangling compatible with the mangling format, then we'd get it for free. The issue is that the manged kernel name needs to contain something pseudo-unique (We use the file's inode + the line number currently). Everything else like `__omp_offloading` isn't strictly necessary AFAIK.

https://github.com/llvm/llvm-project/pull/101400