Make the liburing header files again compatible with C++

Include <atomic> instead of <stdatomic.h> if built with a C++ compiler.

Fixes: b9c0bf79aa87 ("src/include/liburing/barrier.h: Use C11 atomics")
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
3 files changed