Add ck_pr_fence_acquire/release to generic GCC version

Signed-off-by: Marcin Juszkiewicz <mjuszkiewicz@redhat.com>
Add AArch64 (64-bit ARM) support

Signed-off-by: Marcin Juszkiewicz <mjuszkiewicz@redhat.com>
Merge pull request #14 from hrw/master

Add preliminary AArch64 support

- Need to investigate ck_epoch hang.