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

[Devon Loehr via llvm-commits]

DKLoehr wrote:

> I think it's reasonable to expect that a single pattern does not mix \ / as a path separator in the same pattern.

This does seem reasonable. It is entirely _valid_ to do so according to the current format, since paths can in fact contain both \ / as separators. However, I'd expect that any file which is aware of the problem would be using the ugly `{\\,/}` syntax to work around the problem, so I doubt this will break much downstream.

> So, on windows we match the path as is, and then also match the converted version.

It does have the downside that now we have to check every path twice on windows, though. I would expect the rule should instead be "if the pattern has backslashes, match \ / exactly; otherwise, treat / as matching both".

I'll look into updating the PR to do that unless there are any objections, though it's been a while so I'll have to remember everything I was doing.

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