[clang] [Clang] Emit LLVM flatten attribute instead of per-callsite alwaysinline (PR #188615)

[Nico Weber via cfe-commits]

nico wrote:

> Will revert if the fix doesn't land soon.

Next time, please revert first and then reland with fix later. HEAD was broken for quite a while, leading us (chromium) to independently re-bisect this crash, only to discover it was already reported. To minimize such duplicate work, LLVM tries to keep HEAD green. See https://llvm.org/docs/DeveloperPolicy.html#revert-policy, in particular the "When should you revert your own change?" section 🙂

https://github.com/llvm/llvm-project/pull/188615