WIN32: hint noreturn functions

apply __declspec(noreturn) compiler hints to functions that
do not return.

Change-Id: I3c6c4703c7235d1df3e21dccad5272ea4cddfd36

lib/roken/errx.c

@@ -35,7 +35,7 @@
 
 #include "err.h"
 
-ROKEN_LIB_FUNCTION void ROKEN_LIB_CALL
+ROKEN_LIB_NORETURN_FUNCTION void ROKEN_LIB_CALL
 errx(int eval, const char *fmt, ...)
 {
   va_list ap;