Won't compile YSFLIGHT under modern GCC

[cptwilson]

In /src/ysclass11/src/ysthreadpool.cpp, #include <cstdio> needs to be declared.
At least for compilation with GCC 13.1.1. Its a simple fix.

It compiles, except now it segfaults and the console output makes me think it might have something to due with using pipewire and not ALSA, but thats a different issue I'll look into later. At least I got it to compile.