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

[Orlando Cazalet-Hyams via cfe-commits]

OCHyams wrote:

I've not fully made up an opinion on this (which is partially why it's taken me a while to get to, sorry about they delay) - I think discussing it could help. (This is possibly this something that should be discussed on Discourse as although it doesn't seem too radical it does feels like a slightly "creative" use of DWARF?).

Some quick thoughts/questions -
* Macros are sort of a similar situation with substitution. I feel that classifying that sort of substitution as inlining would be misleading, where is the line? Does this really want a non-existent alternative DWARF feature instead?
* Out of curiosity what does GCC (or other compilers) do?
* Question about the impl, what source location do you use for the "inlined" instruction? If a user steps-in to one of these "inlined" functions, what does the debugger show/where do they "go"?

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