[llvm][Support][Windows] Fix slash in path for remove_directories

Before 925471e remove_directories
supports path with slash (instead of backslash).
The ILCreateFromPathW in new implementation requirs backslash path,
so the call to remove_directories will fail if the path contains slash.

This is to normalize the path to make sure remove_directories still
support path with slash as well.

Author: jsji

llvm/lib/Support/Windows/Path.inc

@@ -1373,9 +1373,11 @@ std::error_code closeFile(file_t &F) {
 }
 
 std::error_code remove_directories(const Twine &path, bool IgnoreErrors) {
+  SmallString<128> NativePath;
+  llvm::sys::path::native(path, NativePath, path::Style::windows_backslash);
   // Convert to utf-16.
   SmallVector<wchar_t, 128> Path16;
-  std::error_code EC = widenPath(path, Path16);
+  std::error_code EC = widenPath(NativePath, Path16);
   if (EC && !IgnoreErrors)
     return EC;