Fix intrin.h b0rkage with older MSVC

Reported by Jonathan Kew.

src/hb-object-private.hh

@@ -63,7 +63,7 @@ typedef volatile int hb_atomic_int_t;
 #define hb_atomic_int_set(AI, V)	g_atomic_int_set (&(AI), V)
 
 
-#elif defined(_MSC_VER)
+#elif _MSC_VER >= 1600
 
 #include <intrin.h>
 
@@ -75,7 +75,11 @@ typedef long hb_atomic_int_t;
 
 #else
 
+#ifdef _MSC_VER
+#pragma message("Could not find any system to define atomic_int macros, library will NOT be thread-safe")
+#else
 #warning "Could not find any system to define atomic_int macros, library will NOT be thread-safe"
+#endif
 
 typedef volatile int hb_atomic_int_t;
 #define hb_atomic_int_add(AI, V)	((AI) += (V), (AI) - (V))