Cleanup tests/core/pthread/create. NFC.

Mostly convert to C to match the other tests here.

See #3494

tests/core/pthread/create.c

diff --git a/tests/core/pthread/create.cpp b/tests/core/pthread/create.c
similarity index 72%
rename from tests/core/pthread/create.cpp
rename to tests/core/pthread/create.c
index 5608dc8..7b35eca 100644
--- a/tests/core/pthread/create.cpp
+++ b/tests/core/pthread/create.c
@@ -3,25 +3,25 @@
 // University of Illinois/NCSA Open Source License.  Both these licenses can be
 // found in the LICENSE file.
 
+#include <stdatomic.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <pthread.h>
 #include <assert.h>
 #include <emscripten.h>
 
-#include <atomic>
 
 #define NUM_THREADS 2
 #define TOTAL 100
 
-static std::atomic<int> sum;
+static _Atomic int sum;
 
 void *ThreadMain(void *arg) {
   for (int i = 0; i < TOTAL; i++) {
     sum++;
     // wait for a change, so we see interleaved processing.
-    int last = sum.load();
-    while (sum.load() == last) {}
+    int last = sum;
+    while (sum == last) {}
   }
   pthread_exit((void*)TOTAL);
 }
@@ -30,38 +30,39 @@
 
 void CreateThread(int i)
 {
-  static int counter = 1;
-  int rc = pthread_create(&thread[i], nullptr, ThreadMain, (void*)i);
+  int rc = pthread_create(&thread[i], NULL, ThreadMain, (void*)i);
   assert(rc == 0);
 }
 
-void mainn() {
+void main_iter() {
   static int main_adds = 0;
-  int worker_adds = sum.load() - main_adds;
+  int worker_adds = sum - main_adds;
   sum++;
   main_adds++;
   printf("main iter %d : %d\n", main_adds, worker_adds);
   if (worker_adds == NUM_THREADS * TOTAL) {
     printf("done!\n");
 #ifndef ALLOW_SYNC
-  emscripten_cancel_main_loop();
+    emscripten_cancel_main_loop();
 #else
-  exit(0);
+    exit(0);
 #endif
   }
 }
 
 int main() {
   // Create initial threads.
-  for(int i = 0; i < NUM_THREADS; ++i) {
+  for (int i = 0; i < NUM_THREADS; ++i) {
     CreateThread(i);
   }
 
   // if we don't allow sync pthread creation, the event loop must be reached for
   // the worker to start up.
 #ifndef ALLOW_SYNC
-  emscripten_set_main_loop(mainn, 0, 0);
+  emscripten_set_main_loop(main_iter, 0, 0);
 #else
-  while (1) mainn();
+  while (1) {
+    main_iter();
+  }
 #endif
 }

tests/test_core.py

diff --git a/tests/test_core.py b/tests/test_core.py
index af177d2..633c377 100644
--- a/tests/test_core.py
+++ b/tests/test_core.py
@@ -8103,28 +8103,30 @@
 
   @node_pthreads
   def test_pthread_create(self):
-    self.do_run_in_out_file_test('tests', 'core', 'pthread', 'create.cpp')
+    self.do_run_in_out_file_test('tests', 'core', 'pthread', 'create.c')
 
   @node_pthreads
   def test_pthread_create_pool(self):
     # with a pool, we can synchronously depend on workers being available
     self.set_setting('PTHREAD_POOL_SIZE', '2')
     self.emcc_args += ['-DALLOW_SYNC']
-    self.do_run_in_out_file_test('tests', 'core', 'pthread', 'create.cpp')
+    self.do_run_in_out_file_test('tests', 'core', 'pthread', 'create.c')
 
   @node_pthreads
   def test_pthread_create_proxy(self):
     # with PROXY_TO_PTHREAD, we can synchronously depend on workers being available
     self.set_setting('PROXY_TO_PTHREAD', '1')
     self.emcc_args += ['-DALLOW_SYNC']
-    self.do_run_in_out_file_test('tests', 'core', 'pthread', 'create.cpp')
+    self.do_run_in_out_file_test('tests', 'core', 'pthread', 'create.c')
 
   @node_pthreads
-  def test_pthread_create_embind_stack_check(self):
+  def test_pthread_embind_stack_check(self):
     # embind should work with stack overflow checks (see #12356)
     self.set_setting('STACK_OVERFLOW_CHECK', 2)
     self.emcc_args += ['--bind']
-    self.do_run_in_out_file_test('tests', 'core', 'pthread', 'create.cpp')
+    # compile with C++ compiler since bind needs C++ stdlibs.
+    shutil.copyfile(path_from_root('tests', 'core', 'pthread', 'create.c'), 'create.cpp')
+    self.do_runf('create.cpp', 'done!')
 
   @node_pthreads
   def test_pthread_exceptions(self):
@@ -8135,13 +8137,11 @@
   def test_emscripten_atomics_stub(self):
     self.do_run_in_out_file_test('tests', 'core', 'pthread', 'emscripten_atomics.c')
 
-  @no_asan('incompatibility with atomics')
   @node_pthreads
   def test_emscripten_atomics(self):
     self.set_setting('USE_PTHREADS', '1')
     self.do_run_in_out_file_test('tests', 'core', 'pthread', 'emscripten_atomics.c')
 
-  @no_asan('incompatibility with atomics')
   @node_pthreads
   def test_emscripten_futexes(self):
     self.set_setting('USE_PTHREADS', '1')