message: Fix gcc build for r291756
  I have accidentally added extra llvm:: namespace qualification.
diff: @@ -302,7 +302,7 @@ protected:
  } // namespace lldb_private
  namespace llvm {
  -template <> struct llvm::format_provider<lldb_private::Error> {
  +template <> struct format_provider<lldb_private::Error> {
  static void format(const lldb_private::Error &error, llvm::raw_ostream &OS,
  llvm::StringRef Options) {
  llvm::format_provider<llvm::StringRef>::format(error.AsCString(), OS,
  