Fix some issues with the OSX port

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/helpers.h b/helpers.h
index 61a3f2b..4f8cc0c 100644
--- a/helpers.h
+++ b/helpers.h
@@ -1,6 +1,8 @@
 #ifndef FIO_HELPERS_H
 #define FIO_HELPERS_H
 
+#include "compiler/compiler.h"
+
 struct in_addr;
 
 extern int __weak posix_memalign(void **ptr, size_t align, size_t size);