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/intcmp.c

@@ -19,10 +19,8 @@
 #include <errno.h> /* errno */
 #include <stdio.h> /* fprintf(3), stderr */
 #include <stdlib.h> /* strtol(3), size_t, EXIT_FAILURE */
-#ifndef EX_USAGE
-#	define EX_USAGE EXIT_FAILURE
-#endif
 #include <unistd.h> /* getopt(3), optind */
+#include <sysexits.h>
 
 /* 0b00? */		/*                     Equal | -e  | 0b001 | 1 */
 #define EQUAL	0x01	/*                   Greater | -g  | 0b010 | 2 */