Add basic/empty test of C++ threads. NFC. (#13237)

Author: sbc100

tests/pthread/test_pthread_cxx_threads.cpp

@@ -0,0 +1,6 @@
+#include <thread>
+
+int main() {
+  std::thread([]{}).join();
+  return 0;
+}

tests/pthread/test_pthread_cxx_threads.out

@@ -8080,6 +8080,13 @@ def test_pthread_c11_threads(self):
       self.set_setting('INITIAL_MEMORY', '64mb')
     self.do_run_in_out_file_test('tests', 'pthread', 'test_pthread_c11_threads.c')
 
+  @node_pthreads
+  def test_pthread_cxx_threads(self):
+    self.set_setting('PROXY_TO_PTHREAD')
+    self.clear_setting('ALLOW_MEMORY_GROWTH')
+    self.set_setting('EXIT_RUNTIME')
+    self.do_run_in_out_file_test('tests', 'pthread', 'test_pthread_cxx_threads.cpp')
+
   @node_pthreads
   def test_pthread_create_pool(self):
     # with a pool, we can synchronously depend on workers being available