Include errno.h instead of defining errno as extern int.

cig/libcig1.c

@@ -8,6 +8,7 @@
 #include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <errno.h>
 
 #define Malloc(type,n)	((type *) malloc(sizeof(type)*(n)))
 #define Free(p)		(free((char *)(p)))
@@ -42,7 +43,6 @@ char *scheme2c_strcpy(s48_value sstr)
 {
     char *result;
     int slen;
-    extern int errno;
 
     slen = S48_STRING_LENGTH(sstr);
     result = Malloc(char, slen+1);