Atomics: Use system headers directly, without bad level dependency to BLI

This will make it easier to re-use library as-is in other projects,
such as Cycles standalone repo for example.

intern/atomic/intern/atomic_ops_utils.h

@@ -52,8 +52,8 @@
 #ifndef __ATOMIC_OPS_UTILS_H__
 #define __ATOMIC_OPS_UTILS_H__
 
-/* needed for int types */
-#include "../../../source/blender/blenlib/BLI_sys_types.h"
+#include <stdint.h>
+#include <stddef.h>
 #include <stdlib.h>
 #include <limits.h>