Changes required for aarch64 support in boost::config.

checks/architecture/arm.cpp

@@ -8,6 +8,8 @@
 
 #if !defined(__arm__) && !defined(__thumb__) && \
     !defined(__TARGET_ARCH_ARM) && !defined(__TARGET_ARCH_THUMB) && \
-    !defined(_ARM) && !defined(_M_ARM)
+    !defined(_ARM) && !defined(_M_ARM) && \
+    !defined(__aarch64__) 
 #error "Not ARM"
 #endif
+