Add EILSEQ errno value.

This is required by C95 and later; it may be set by character/string conversion functions. Note that the value of 12 conflicts with GNO's existing definition of EPERM. This should not cause much trouble, but GNO could potentially define its own different value for EILSEQ, with the GNO version of ORCALib adjusted accordingly.

ORCACDefs/errno.h

@@ -25,6 +25,7 @@
 #define EACCESS                 9       /* alias for EACCES */
 #define EEXIST                  10      /* the file exists */
 #define ENOSPC                  11      /* the file is too large */
+#define EILSEQ                  12      /* encoding error */
 
 extern int errno;
 #define errno errno