lib/krb5: WIN32 disable warnings

Heimdal declares functions that never return as non-void.  Suppress
the following warnings now that functions are labeled 'noreturn'.

4646 - function declared with __declspec(noreturn) has non-void return type

4716 - 'function' must return a value

Change-Id: Id85cc435e99688bae7326a723a5a80d828859bf2

lib/krb5/warn.c

@@ -31,6 +31,11 @@
  * SUCH DAMAGE.
  */
 
+#if defined(_MSC_VER)
+# pragma warning(disable: 4646)
+# pragma warning(disable: 4716)
+#endif
+
 #include "krb5_locl.h"
 #include <err.h>