Summary:
[Folly] Replace `FOLLY_HAVE_LINUX_MEMBARRIER_H` with `__has_include`.

Now that folly only targets which support `__has_include`.

Reviewed By: Orvid

Differential Revision: D9279852

fbshipit-source-id: 94c446a2d6e2662d32a7899ab470679da6da8e0e