Tests: Build automatically, fix compilation errors

Userland/Tests/Kernel/null-deref-crash-during-pthread_join.cpp

@@ -0,0 +1,21 @@
+#include <pthread.h>
+#include <stdio.h>
+#include <sys/select.h>
+#include <unistd.h>
+
+int main(int, char**)
+{
+    pthread_t tid;
+    pthread_create(
+        &tid, nullptr, [](void*) -> void* {
+            sleep(1);
+            asm volatile("ud2");
+            return nullptr;
+        },
+        nullptr);
+
+    pthread_join(tid, nullptr);
+
+    printf("ok\n");
+    return 0;
+}