add two extra noreturn that clang picked up

Signed-off-by: Rosen Penev <rosenp@gmail.com>

src/input/InputStream.cxx

@@ -68,6 +68,7 @@ InputStream::CheapSeeking() const noexcept
 	return IsSeekable() && !ExpensiveSeeking(uri.c_str());
 }
 
+//[[noreturn]]
 void
 InputStream::Seek(std::unique_lock<Mutex> &, [[maybe_unused]] offset_type new_offset)
 {