There is code that only expects to be compiled with clang++ and uses its
<stdatomic.h>, which works because Clang supports the _Atomic specifier
in C++. The addition of <stdatomic.h> to libstdc++ broke this code, as
now it finds the C++ header instead, which is empty for any standard
mode before C++23.
This change allows that code to keep working as before, by forwarding to
clang's <stdatomic.h>.
libstdc++-v3/ChangeLog:
* include/c_compatibility/stdatomic.h [__clang__]: Use
#include_next <stdatomic.h>.
using std::atomic_thread_fence;
using std::atomic_signal_fence;
+#elif defined __clang__
+# include_next <stdatomic.h>
#endif // C++23
#endif // _GLIBCXX_STDATOMIC_H