[Headers] Add a test for arm64intr.h

This tests the ARM64 specific constants added in SVN r309081,
similar to the one added in r277928 for armintr.h.

Differential Revision: https://reviews.llvm.org/D35934

llvm-svn: 309314

clang/test/Headers/ms-intrin.cpp

@@ -64,4 +64,8 @@ void f() {
 #ifdef _M_ARM
   __dmb(_ARM_BARRIER_ISHST);
 #endif
+
+#ifdef _M_ARM64
+  __dmb(_ARM64_BARRIER_SY);
+#endif
 }