GNUmakefile, intcmp(1), npc(1), scrut(1), str(1), strcmp(1), include/sysexits.h: added fallback header file for when systems don’t have sysexits.h(3)

src/npc.c

@@ -20,12 +20,7 @@
                     * EOF */
 #include <stdlib.h> /* EXIT_FAILURE, EXIT_SUCCESS */
 #include <unistd.h> /* getopt(3) */
-#if !defined EX_USAGE
-#	define EX_USAGE EXIT_FAILURE
-#endif
-#if !defined EX_OK
-#	define EX_OK EXIT_SUCCESS
-#endif
+#include <sysexits.h>
 
 int main(int argc, char *argv[]){
 	int c;