[llvm] [Support] Add LLVM_WINDOWS_AVOID_SHELL32_APIS for shell32-free path lookups (PR #209448)

[Aaron Ballman via llvm-commits]

AaronBallman wrote:

> Removing the `IShellOperation` for `remove_directories` is possible, it's just that the cost is complexity for us. The `IShellOperation` can do various things including recursive upward traversal for removal, error recovery, atomic operations etc. all of that can be redone manually with `RemoveDirectoryW`, but it's totally feasible. The KF removal I don't know a good way around.

So I suppose the question should be asked: do we want any changes here at all? Is:

> so any binary that embeds LLVM and is validated against that surface (UWP / sandboxed apps, Windows drivers; e.g. via ApiValidator) is rejected for importing it.

a use case we want to support? I can imagine folks wanting a sandboxed compiler (we know about plenty of things like godbolt, ideone, wandbox, etc) so I was assuming we do want a change here, but is the maintenance cost looking high enough we need community buy-in for the use case? (Also, are there other changes needed for other libraries or is Shell32 the only things we have to worry about to meet the need?)

https://github.com/llvm/llvm-project/pull/209448