Add simple test for CI build workflow

test/error.cpp

@@ -0,0 +1,12 @@
+/**
+ * Demonstrate that we can compile, link, and run an application
+ * with libzt and successfully get an error from the socket API.
+ */
+
+#include <cstdlib>
+#include <ZeroTierSockets.h>
+
+int main()
+{
+	return zts_socket(0,0,0) != -2; // We expect -2 from an uninitialized libzt instance
+}