[clang] [llvm] [Clang] Show inlining hints for __attribute__((warning/error)) (PR #174892)

[Justin Stitt via cfe-commits]

JustinStitt wrote:

@nickdesaulniers Are you suggesting removing the flag `-fdiagnostics-show-inlining-chain` **as well as** the heuristic mode and just have `-gline-directives-only` enable these hints (With a meta hint about -g1 or greater on the WarningAttr itself)?

I am all for removing the flag but the accuracy of the heuristic mode seems to be pretty good and judging from my benchmarking it has no impact on build times. I know some folks have complained about the memory usage of full LLVM builds so perhaps I should benchmark to see if there is a measurable memory usage increase. I imagine the peak memory usage occurs during linking and all the `srcloc` is gone by then so I don't forsee any increase in peak memory usage.

I reckon we can remove the flag `-fdiagnostics-show-inlining-chain` and have the heuristic mode on by default with the meta hint about `-gline-directives-only` which, if enabled, would turn some better tracking utilizing the debug info.

https://github.com/llvm/llvm-project/pull/174892