OSMemoryBarrier() deprecated in OSX 10.12

[ahxxm]

compiler suggests to use std::atomic_thread_fence() instead:

In file included from ./port/port_posix.h:47:
./port/atomic_pointer.h:59:3: warning: 'OSMemoryBarrier' is deprecated: first deprecated in macOS 10.12 - Use
      std::atomic_thread_fence() from <atomic> instead [-Wdeprecated-declarations]
  OSMemoryBarrier();
  ^
/usr/include/libkern/OSAtomicDeprecated.h:749:9: note: 'OSMemoryBarrier' has been explicitly marked deprecated here
void    OSMemoryBarrier( void );
        ^
1 warning generated.

[droark]

I filed a patch for this warning.

[pwnall]

Fixed in 594cc98. Sorry this took a while!