Add test for sequential consistency in printing from a pthread.

test/pthread/test_pthread_print_seq_consistent.c

@@ -0,0 +1,19 @@
+// Copyright 2025 The Emscripten Authors.  All rights reserved.
+// Emscripten is available under two separate licenses, the MIT license and the
+// University of Illinois/NCSA Open Source License.  Both these licenses can be
+// found in the LICENSE file.
+
+#include <pthread.h>
+#include <emscripten/console.h>
+
+void *pthread_main(void *arg) {
+  emscripten_out("thread has started.");
+  return 0;
+}
+
+int main() {
+  pthread_t t;
+  pthread_create(&t, 0, pthread_main, 0);
+  pthread_join(t, 0);
+  emscripten_out("thread joined");
+}

test/pthread/test_pthread_print_seq_consistent.js

@@ -0,0 +1,3 @@
+if (!ENVIRONMENT_IS_PTHREAD) {
+  Module.print = (text) => { console.log(text); }
+}

test/pthread/test_pthread_print_seq_consistent.out

@@ -0,0 +1,2 @@
+thread has started.
+thread joined

test/test_core.py

@@ -2761,6 +2761,17 @@ def test_pthread_run_on_main_thread(self):
       self.skipTest('MINIMAL_RUNTIME + threads + asan does not work')
     self.do_run_in_out_file_test('pthread/test_pthread_run_on_main_thread.c')
 
+  # This test verifies that printing from a pthread has sequential consistency.
+  @node_pthreads
+  @parameterized({
+    '': ([],),
+    'print_override': (['--pre-js', test_file('pthread/test_pthread_print_seq_consistent.js')],),
+  })
+  def test_pthread_print_seq_consistent(self, cflags):
+    self.skipTest('Currently broken due to https://github.com/emscripten-core/emscripten/issues/19683')
+    self.do_run_in_out_file_test('pthread/test_pthread_print_seq_consistent.c',
+      cflags=cflags)
+
   def test_tcgetattr(self):
     self.do_runf('termios/test_tcgetattr.c', 'success')