[clang] [llvm] [clang][Inliner] Add opt-in inliner hints for lambdas and main-file functions (PR #228074)

[Kuba Mracek via cfe-commits]

kubamracek wrote:

> I'm not convinced this is something we want to do for "main-file" functions. What kind of inlining behavior you want for "main-file" functions is going to heavily depend upon how you write your application. For something like a server application, people generally do not care about what's in the main file.

I think I might have managed to introduce a confusion here (and I'll rename the PR and description to avoid that confusion) -- code being from "main-file" in this PR means it's coming from *any* .cpp file and it's not coming from a \#include'd .h file. It's not about anything like main.cpp or "the file that contains main()".

https://github.com/llvm/llvm-project/pull/228074