Configure: set default cacheline size to 64 for aarch64 platforms.

auto/os/conf

diff --git a/auto/os/conf b/auto/os/conf
index 6096af5..7c6cb69 100644
--- a/auto/os/conf
+++ b/auto/os/conf
@@ -110,6 +110,11 @@
         NGX_MACH_CACHE_LINE=64
     ;;
 
+    aarch64 )
+        have=NGX_ALIGNMENT value=16 . auto/define
+        NGX_MACH_CACHE_LINE=64
+    ;;
+
     *)
         have=NGX_ALIGNMENT value=16 . auto/define
         NGX_MACH_CACHE_LINE=32