third_party/libcxxabi: Enable __cxa_thread_atexit

Enable `__cxa_thread_atexit` from libcxxabi.
`__cxa_thread_atexit_impl` is still implemented by the cosmo libc.
The original `__cxa_thread_atexit` has been removed.

libc/thread/__cxa_thread_atexit.c

@@ -1,23 +0,0 @@
-/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
-│ vi: set et ft=c ts=2 sts=2 sw=2 fenc=utf-8                               :vi │
-╞══════════════════════════════════════════════════════════════════════════════╡
-│ Copyright 2023 Justine Alexandra Roberts Tunney                              │
-│                                                                              │
-│ Permission to use, copy, modify, and/or distribute this software for         │
-│ any purpose with or without fee is hereby granted, provided that the         │
-│ above copyright notice and this permission notice appear in all copies.      │
-│                                                                              │
-│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
-│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
-│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
-│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
-│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
-│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
-│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
-│ PERFORMANCE OF THIS SOFTWARE.                                                │
-╚─────────────────────────────────────────────────────────────────────────────*/
-#include "libc/intrin/cxaatexit.internal.h"
-
-int __cxa_thread_atexit(void *fun, void *arg, void *dso_symbol) {
-  return __cxa_thread_atexit_impl(fun, arg, dso_symbol);
-}

test/libc/thread/BUILD.mk

@@ -41,6 +41,7 @@ TEST_LIBC_THREAD_DIRECTDEPS =				\
 	LIBC_THREAD					\
 	LIBC_TIME					\
 	LIBC_X						\
+	THIRD_PARTY_LIBCXXABI				\
 	THIRD_PARTY_NSYNC				\
 	THIRD_PARTY_NSYNC_MEM
 

third_party/libcxxabi/BUILD.mk

@@ -90,6 +90,7 @@ $(THIRD_PARTY_LIBCXXABI_A_OBJS): private				\
 			-frtti						\
 			-D_LIBCXXABI_BUILDING_LIBRARY			\
 			-D_LIBCPP_BUILDING_LIBRARY			\
+			-DHAVE___CXA_THREAD_ATEXIT_IMPL			\
 			-D_LIBCPP_CONSTINIT=__constinit			\
 			-Dconstinit=__constinit
 

third_party/libcxxabi/README.cosmo

@@ -15,3 +15,4 @@ LOCAL CHANGES
 
   - Add <__memory/aligned_alloc.h> (contains a few inline functions) from
   upstream libcxx.
+  - Enable __cxa_thread_atexit for Cosmopolitan.

third_party/libcxxabi/include/cxxabi.h

@@ -160,7 +160,7 @@ __cxa_decrement_exception_refcount(void *primary_exception) throw();
 extern _LIBCXXABI_FUNC_VIS bool __cxa_uncaught_exception() throw();
 extern _LIBCXXABI_FUNC_VIS unsigned int __cxa_uncaught_exceptions() throw();
 
-#if defined(__linux__) || defined(__Fuchsia__)
+#if defined(__linux__) || defined(__Fuchsia__) || defined(__COSMOPOLITAN__)
 // Linux and Fuchsia TLS support. Not yet an official part of the Itanium ABI.
 // https://sourceware.org/glibc/wiki/Destructor%20support%20for%20thread_local%20variables
 extern _LIBCXXABI_FUNC_VIS int __cxa_thread_atexit(void (*)(void *), void *,