userland: move some multithreaded examples from cpp-cheat

Using them mostly to evaluate how well the emulators are handling user
mode multithreading.

userland/cpp/thread_hardware_concurrency.cpp

@@ -0,0 +1,10 @@
+// http://stackoverflow.com/questions/150355/programmatically-find-the-number-of-cores-on-a-machine
+//
+// Not affected by taskset: https://stackoverflow.com/questions/1006289/how-to-find-out-the-number-of-cpus-using-python/55423170#55423170
+
+#include <iostream>
+#include <thread>
+
+int main() {
+    std::cout << std::thread::hardware_concurrency() << std::endl;
+}