Correct definition of ATTRIBUTE_NORETURN on Windows.

Only microsoft compiler, which can be correctly
tested with #ifdef _MSC_VER) has __declspec(noreturn)

include/my_compiler.h

@@ -161,7 +161,7 @@ marked as unlikely by the branch prediction mechanism.  optimize a
 rarely invoked function for size instead for speed. */
 #  define ATTRIBUTE_COLD __attribute__((cold))
 # endif
-#elif defined _WIN32
+#elif defined _MSC_VER
 # define ATTRIBUTE_NORETURN __declspec(noreturn)
 #else
 # define ATTRIBUTE_NORETURN /* empty */