[clang] [llvm] Make sanitizer special case list slash-agnostic (PR #149886)

[Devon Loehr via llvm-commits]

DKLoehr wrote:

> Maybe we should do some variant of #!special-case-list-v1 for this change too? (#!canonical-paths?)

I like this, because it makes it helps avoid the weirdness problem where `foo\\bar` will stop matching if we canonicalize paths. Having that line in the file gives a visual marker of what's happening.

(As a side note, perhaps we should get rid of the v1 line? At least in theory it was slated for removal two versions ago.)

https://github.com/llvm/llvm-project/pull/149886