[clang] [compiler-rt] [sanitizer] Add DoubleFreeSanitizer (DSan) (PR #213846)

[Bojun Seo via cfe-commits]

Bojun-Seo wrote:

Agreed, let's keep the design discussion on the forum rather than here.

One note so it does not get lost with the RFC: this branch is the stand-alone LeakSanitizer alternative to the DSan runtime, so it opens with a revert of that commit and ends with the LSan implementation. The two commits in between are pre-existing realloc() bugs that still reproduce on main and are independent of this proposal. I am happy to send them as a separate pull request if that is easier to review.

https://github.com/llvm/llvm-project/pull/213846