[libcxx-commits] [libcxxabi] [libc++abi] Revert gating of `__cxa_thread_atexit` on Linux||Fuchsia (PR #186054)

[via libcxx-commits]

https://github.com/whitequark updated https://github.com/llvm/llvm-project/pull/186054

>From 1924b876d2f28d57e8277207864b63187055feb6 Mon Sep 17 00:00:00 2001
From: Catherine <whitequark at whitequark.org>
Date: Thu, 12 Mar 2026 08:19:49 +0000
Subject: [PATCH] [libc++abi] Revert gating of `__cxa_thread_atexit` on
 Wasm/WASI

This was done in the commit 3c100d5d548d with the description
"Enable -Wmissing-prototypes" which seems incongruent to me.

Since then it's made its way into a release and broke the use of
`thread_local` variables with destructors on Wasm/WASI:

```cc
// repro.cc
struct c { ~c() {} };
thread_local c v;
int main() { (void)v; }
```

```console
$ ./wasi-sdk-31.0-x86_64-linux/bin/clang++ repro.cc
wasm-ld: error: /tmp/repro-dd1ad7.o: undefined symbol: __cxa_thread_atexit
clang++: error: linker command failed with exit code 1 (use -v to see invocation)
```
---
 libcxxabi/src/cxa_thread_atexit.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libcxxabi/src/cxa_thread_atexit.cpp b/libcxxabi/src/cxa_thread_atexit.cpp
index 402a52c741012..7eaee8cfc1612 100644
--- a/libcxxabi/src/cxa_thread_atexit.cpp
+++ b/libcxxabi/src/cxa_thread_atexit.cpp
@@ -106,7 +106,7 @@ namespace {
 
 #endif // HAVE___CXA_THREAD_ATEXIT_IMPL
 
-#if defined(__linux__) || defined(__Fuchsia__)
+#if defined(__linux__) || defined(__Fuchsia__) || defined(__wasm__)
 extern "C" {
 
   _LIBCXXABI_FUNC_VIS int __cxa_thread_atexit(Dtor dtor, void* obj, void* dso_symbol) throw() {
@@ -141,6 +141,6 @@ extern "C" {
     }
 #endif // HAVE___CXA_THREAD_ATEXIT_IMPL
   }
+#endif // defined(__linux__) || defined(__Fuchsia__) || defined(__wasm__)
 } // extern "C"
-#endif // defined(__linux__) || defined(__Fuchsia__)
 } // namespace __cxxabiv1