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

[via llvm-commits]

ustachow wrote:

@compnerd are you comfortable proceeding? For context, in our use case these functions are never actually called, we only need the shell32 import gone.

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