Added unistd.h and some linux syscall wrappers

tests/start.c

@@ -1,7 +1,9 @@
+#include <unistd.h>
 #include <stdio.h>
-#include <stdint.h>
 
 int main(int argc, char **argv)
 {
-    return 42;
+    const char *msg = "Hello!\n";
+    write(fileno(stdout), msg, 7);
+    return 0;
 }