This makes them pass standalone compilation tests. Previously,
they included atomic.h which included themselves again, leading to
double definitions.
Signed-off-by: Martin Storsjö <martin@martin.st>
These could be used for reference counting, or for keeping track of
decoding progress in references in multithreaded decoders.
Support is provided by gcc/msvc/suncc intrinsics, with a fallback using
pthread mutexes.
Signed-off-by: Anton Khirnov <anton@khirnov.net>
