Enable build for aarch64.
diff --git a/ref_vmul_n.c b/ref_vmul_n.c
index d88542a..390e657 100644
--- a/ref_vmul_n.c
+++ b/ref_vmul_n.c
@@ -23,7 +23,7 @@
 
 */
 
-#ifdef __arm__
+#if defined(__arm__) || defined(__aarch64__)
 #include <arm_neon.h>
 #else
 #include "stm-arm-neon.h"