move sync headers from include to libsync

Make sw_sync.h private

Change-Id: I0b120ebe81fd4a191b7aa4b6a8de4f64d16e2b3e
diff --git a/libsync/sync_test.c b/libsync/sync_test.c
index 386747a..ee9ea3c 100644
--- a/libsync/sync_test.c
+++ b/libsync/sync_test.c
@@ -23,6 +23,7 @@
 #include <unistd.h>
 
 #include <sync/sync.h>
+#include "sw_sync.h"
 
 pthread_mutex_t printf_mutex = PTHREAD_MUTEX_INITIALIZER;