More new AIX errors

[David Edelsohn]

Hi, Jonathan

Thanks for the recent fixes.  I still see a few errors that have crept
in on AIX.  All the same:

FAIL: 17_intro/headers/c++2020/all_no_rtti.cc (test for excess errors)
FAIL: 17_intro/headers/c++2020/all_pedantic_errors.cc (test for excess errors)
FAIL: 17_intro/headers/c++2020/operator_names.cc (test for excess errors)
FAIL: 17_intro/headers/c++2020/stdc++.cc (test for excess errors)
FAIL: 17_intro/headers/c++2020/stdc++_multiple_inclusion.cc (test for
excess errors)

/tmp/GCC/powerpc-ibm-aix7.2.3.0/libstdc++-v3/include/latch:64: error:
'notify_all' is not a member of 'std::__atomic_impl'
/tmp/GCC/powerpc-ibm-aix7.2.3.0/libstdc++-v3/include/latch:75: error:
'__atomic_wait' is not a member of 'std'; did you mean
'__atomic_val_t'?

Can you take a look when you have a moment?

Thanks, David