8993 sync regcomp(3C) with upstream

@@ -184,6 +184,7 @@
         sopno nplus;            /* how deep does it nest +s? */
 };
 
 /* misc utilities */
 #define OUT     (CHAR_MIN - 1)  /* a non-character value */
+#define IGN     (CHAR_MIN - 2)
 #define ISWORD(c)       (iswalnum((uch)(c)) || (c) == '_')