add stdnoreturn.h (C11)

features.h contains the fallback logic for pre-C11 compilers

include/stdnoreturn.h

@@ -0,0 +1,5 @@
+#ifndef _STDNORETURN_H
+#define _STDNORETURN_H
+#include <features.h>
+#define noreturn _Noreturn
+#endif