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/str.c

@@ -22,9 +22,7 @@
 #include <stdio.h> /* fprintf(3) */
 #include <stdlib.h> /* EXIT_FAILURE */
 #include <string.h> /* strcmp(3) */
-#if !defined EX_USAGE
-#	define EX_USAGE EXIT_FAILURE
-#endif
+#include <sysexits.h>
 
 static char *program_name = "str";