[clang] [llvm] [sancov] Add -fsanitize-coverage=dataflow-args,dataflow-ret (PR #201410)

[Yunseong Kim via cfe-commits]

yskzalloc wrote:

Thank you @melver for the suggestion. I completely agree that this is substantial enough to warrant an LLVM RFC, and I have already been preparing one for this feature.

I will rewrite and submit the next version of this patch using the `trace-args` and `trace-ret` naming convention, as it aligns much better with LLVM's existing SanitizerCoverage idioms.

https://github.com/llvm/llvm-project/pull/201410