libstdc++: Fix std::atomic<std::shared_ptr<T>> for AIX [PR104101]

This fixes an on AIX.

The lock function currently just spins, which should be changed to use
back-off, and maybe then _M_val.wait(__current) when supported.

libstdc++-v3/ChangeLog:

	PR libstdc++/104101
	* include/bits/shared_ptr_atomic.h (_Sp_atomic::_Atomic_count::lock):
	Only use __thread_relax if __cpp_lib_atomic_wait is defined.

diff --git a/libstdc++-v3/include/bits/shared_ptr_atomic.h b/libstdc++-v3/include/bits/shared_ptr_atomic.h
index 50aa463..35f781d 100644 (file)
--- a/libstdc++-v3/include/bits/shared_ptr_atomic.h
+++ b/libstdc++-v3/include/bits/shared_ptr_atomic.h
@@ -392,7 +392,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
          auto __current = _M_val.load(memory_order_relaxed);
          while (__current & _S_lock_bit)
            {
+#if __cpp_lib_atomic_wait
              __detail::__thread_relax();
+#endif
              __current = _M_val.load(memory_order_relaxed);
            }
 
@@ -401,7 +403,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
                                                 __o,
                                                 memory_order_relaxed))
            {
+#if __cpp_lib_atomic_wait
              __detail::__thread_relax();
+#endif
              __current = __current & ~_S_lock_bit;
            }
          return reinterpret_cast<pointer>(__current);