Nvc++ error with <atomic> and C++20 flag

Hi,

Using nvc++ and the -std=c++2a flag, it seems that including <atomic> will lead to an error with version 21.3 of the HPC SDK:

/usr/include/c++/10/atomic", line 931: error: identifier __GCC_ATOMIC_CHAR8_T_LOCK_FREE" is undefined
static constexpr bool is_always_lock_free = ATOMIC_CHAR8_T_LOCK_FREE == 2;

I’m running Ubuntu 20.10, which I know is unsupported. As a workaround, if I define __GCC_ATOMIC_CHAR8_T_LOCK_FREE to 2, our tests still pass.

It’s great to see C++20 support coming through in nvc++ now.

Best regards,
Paul