[clang] [clang][DebugInfo] Add inlined subprogram metadata for compiler built-ins (PR #189969)

[J. Ryan Stinnett via cfe-commits]

jryans wrote:

The test failures above have highlighted the case of built-ins like `__builtin_unreachable` which exist purely to communicate something to the compiler (and are not acting as regular calls). I believe we would want these to function as before without this artificial call-like inlined debug info.

I think I'll mark this PR a draft for now while I ponder a strategy to apply this more selectively. In the mean time, I am still happy to hear any feedback on the overall idea.

https://github.com/llvm/llvm-project/pull/189969