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

[Marco Elver via llvm-commits]

melver wrote:

> I'm still working on it, but this month’s AI tokens have all been used up. I’ll update the revision work at the beginning of next month.

I think the consensus in [this thread](https://discourse.llvm.org/t/rfc-introduction-of-doublefreesanitizer-dsan/91363/16) was having a dedicated tool that is a subset or very closely overlapping of a range of other tools (ASan, Scudo, GWP-ASan, LSan, etc.) in compiler-rt doesn't make much sense. You've evaluated against the no-instrument-ASan option, but did you manage to prototype the **out-of-tree option**? Why does it need to be part of compiler-rt? Because you do not need compiler instrumentation, the flag `-fsanitize=doublefree` is a convenience and not technically needed, and a pure runtime tool can be standalone out-of-tree.

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