Remove __cxa_thread_atexit stubs (#15531)

Back in #14489 we started using the implemenation of
`__cxa_thread_atexit` from libcxxabi so this is stub should never be
needed.

This change also involves renaming the test from `.c` to `.cpp` since
C programs don't generally have access to `__cxa_thread_atexit` (its
part of libcxxabi).

I also removed the call to `__cxa_thread_atexit_impl` since we don't
define that anywhere in emscripten.

Also run this tests with threads enabled which would have resulted
in an undefined reference to `__cxa_thread_atexit_impl` previously.

Author: sbc100

src/library_pthread_stub.js

@@ -16,9 +16,6 @@ var LibraryPThreadStub = {
     return !ENVIRONMENT_IS_WORKER;
 #endif
   },
-
-  __cxa_thread_atexit: 'atexit',
-  __cxa_thread_atexit_impl: 'atexit',
 };
 
 mergeInto(LibraryManager.library, LibraryPThreadStub);

tests/core/test_atexit_threads.c renamed to tests/core/test_atexit_threads.cpp

@@ -8,8 +8,9 @@
 #include <stdio.h>
 #include <stdlib.h>
 
-extern int __cxa_thread_atexit(void (*dtor)(void *), void *obj, void *dso_symbol);
-extern int __cxa_thread_atexit_impl(void (*dtor)(void *), void *obj, void *dso_symbol);
+extern "C" {
+  int __cxa_thread_atexit(void (*dtor)(void *), void *obj, void *dso_symbol);
+}
 
 static void cleanA() { printf("A\n"); }
 static void cleanB() { printf("B\n"); }
@@ -19,6 +20,5 @@ int main() {
   atexit(cleanA);
   atexit(cleanB);
   __cxa_thread_atexit(cleanCarg, (void*)100, NULL);
-  __cxa_thread_atexit_impl(cleanCarg, (void*)234, NULL);
   return 0;
 }

tests/core/test_atexit_threads.out

@@ -1,4 +1,3 @@
-C 234
 C 100
 B
 A

tests/test_core.py

@@ -2385,10 +2385,15 @@ def test_atexit(self):
       self.set_setting('EXIT_RUNTIME')
     self.do_core_test('test_atexit.c')
 
-  def test_atexit_threads(self):
+  def test_atexit_threads_stub(self):
     # also tests thread exit (__cxa_thread_atexit)
     self.set_setting('EXIT_RUNTIME')
-    self.do_core_test('test_atexit_threads.c')
+    self.do_core_test('test_atexit_threads.cpp')
+
+  @node_pthreads
+  def test_atexit_threads(self):
+    self.set_setting('EXIT_RUNTIME')
+    self.do_core_test('test_atexit_threads.cpp')
 
   @no_asan('test relies on null pointer reads')
   def test_pthread_specific(self):