add stdnoreturn.h (C11)

features.h contains the fallback logic for pre-C11 compilers
diff --git a/include/stdnoreturn.h b/include/stdnoreturn.h
new file mode 100644
index 0000000..60d924a
--- /dev/null
+++ b/include/stdnoreturn.h
@@ -0,0 +1,5 @@
+#ifndef _STDNORETURN_H
+#define _STDNORETURN_H
+#include <features.h>
+#define noreturn _Noreturn
+#endif