2019-03-04 Edward Smith-Rowland <3dw4rd@verizon.net>
PR libstdc++/88996 Implement P0439R0
Make std::memory_order a scoped enumeration.
* include/bits/atomic_base.h: For C++20 make memory_order a scoped enum,
add variables for the old enumerators. Adjust calls.
* testsuite/29_atomics/headers/atomic/types_std_c++2a.cc: New test.
* testsuite/29_atomics/headers/atomic/types_std_c++2a_neg.cc: New test.
From-SVN: r269372
