Most of LLVM code uses the llvm::sys::path::append function to concatenate paths and will get the correct native slash. In some code locations it seems that direct string concatenation was used, possibly because the code writer knows there are no extra path sepeartors to deal with, so string concat was more efficient than append.
In the locations below, the path seperator is hardcoded as '/'. Fixed by exposing the native seperator from llvm::sys:;path and using it.
As an alternative, the append function could be used but it's more code and less efficient.