Emulated TLS is broken under macOS 10.6?

[catap (Kirill A. Korinsky)]

I've installed last macports clangs on my test macOS 10.6 as:

macOS-Snow-Leopard:~ catap$ port installed | grep clang-
  clang-9.0 @9.0.1_4+defaultlibcxx+emulated_tls+libstdcxx
  clang-10 @10.0.1_5+defaultlibcxx+emulated_tls+libstdcxx (active)
  clang-11 @11.1.0_3+defaultlibcxx+emulated_tls+libstdcxx (active)
macOS-Snow-Leopard:~ catap$

Let me create small test to enjoy emulated TLS::

#include <vector>

int main() {
  thread_local std::vector<int> foo;
  return 0;
}

an attemp to build it fails:

macOS-Snow-Leopard:tmp catap$ clang++-mp-11 test.cc 
Undefined symbols for architecture x86_64:
  "___cxa_thread_atexit", referenced from:
      _main in test-d301bb.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
macOS-Snow-Leopard:tmp catap$ clang++-mp-10 test.cc 
Undefined symbols for architecture x86_64:
  "___cxa_thread_atexit", referenced from:
      _main in test-4fab06.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
macOS-Snow-Leopard:tmp catap$ clang++-mp-9.0 test.cc 
Undefined symbols for architecture x86_64:
  "___cxa_thread_atexit", referenced from:
      _main in test-fc4772.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
macOS-Snow-Leopard:tmp catap$ 

[catap (Kirill A. Korinsky)]

Can you closed it, I've missed readme for libcxx.