store errno in SIMPLE-FILE-ERROR conditions

CCL signals SIMPLE-FILE-ERROR conditions for all file-related errors, but they
do not contain any information to programmatically distinguish what the error
actually is.

The most basic use case is the ability to detect that opening a file failed
because it does not exist. Without this patch, it is impossible to make the
difference between a file-not-found error and for example an IO error.

level-1/l1-error-signal.lisp

@@ -45,7 +45,7 @@
 	 (format-string (if errargs
 			  (format nil "~a : ~a" error-string "~s")
 			  error-string)))
-    (%err-disp-common nil err-type  format-string errargs frame-ptr)))
+    (%err-disp-common errno err-type  format-string errargs frame-ptr)))
 
 
 (defun %err-disp-internal (err-num errargs frame-ptr)
@@ -87,7 +87,8 @@
                  (simple-file-error (make-condition condition-name
                                              :pathname (car errargs)
                                              :error-type format-string
-                                             :format-arguments (cdr errargs)))
+                                             :format-arguments (cdr errargs)
+                                             :errno err-num))
                  (undefined-function (make-condition condition-name
                                                      :name (car errargs)))
                  (call-special-operator-or-macro

level-1/l1-error-system.lisp

@@ -580,7 +580,9 @@
                      (file-error-pathname c)))))
 
 (define-condition simple-file-error (simple-condition file-error)
-  ()
+  ((errno
+     :initarg :errno
+     :reader simple-file-error-errno))
   (:report (lambda (c s)
 	     (apply #'format s (slot-value c 'error-type) 
 		    (file-error-pathname c)