Support: Delete copy constructors for RedirectingFileSystem

[tstellar]

Summary

This is necessary to avoid C2280 errors with msvc if we were to add
__declspec(dllexport) to the class.

llvm/include/llvm/Support/VirtualFileSystem.h

private:
 
   /// Determine the prefix directory if the roots are relative paths. See
   /// \c RootRelativeKind for details.
   RootRelativeKind RootRelative = RootRelativeKind::CWD;
   /// @}
 
   RedirectingFileSystem(IntrusiveRefCntPtr<FileSystem> ExternalFS);
 
+  /// Explicitly delete copy constructors.  The unique_ptrs in \c Roots can't
+  /// be copied.
+  RedirectingFileSystem(const RedirectingFileSystem &) = delete;
+  RedirectingFileSystem &operator=(const RedirectingFileSystem &) = delete;
+
   /// Looks up the path <tt>[Start, End)</tt> in \p From, possibly recursing
   /// into the contents of \p From if it is a directory. Returns a LookupResult
   /// giving the matched entry and, if that entry is a FileEntry or
   /// DirectoryRemapEntry, the path it redirects to in the external file system.
   ErrorOr<LookupResult>
   lookupPathImpl(llvm::sys::path::const_iterator Start,
                  llvm::sys::path::const_iterator End, Entry *From,
                  llvm::SmallVectorImpl<Entry *> &Entries) const;