compat: Add shims for the 'shell' module.

* gash/compat.scm [mes] (X_OK): New variable.
[mes] (program-arguments): New procedure.
[mes] (delete-duplicates!): New procedure.
[mes] (flush-all-ports): New procedure.
[mes] (file-port?): New procedure.
[mes] (input-port?): New procedure.
[mes] (output-port?): New procedure.
[mes] (dup): Redefine to support an optional 'new' argument.

gash/compat.scm

@@ -89,7 +89,14 @@
           the-eof-object
           noop
           make-prompt-tag
-          canonicalize-path)
+          canonicalize-path
+          X_OK
+          program-arguments
+          delete-duplicates!
+          flush-all-ports
+          file-port?
+          input-port?
+          output-port?)
 
   (define-macro (define-inlinable . rest)
     `(define ,@rest))
@@ -127,4 +134,26 @@
     (list stem))
 
   ;; XXX: Actually implement this.
-  (define (canonicalize-path path) path))
+  (define (canonicalize-path path) path)
+
+  (define X_OK 1)
+
+  (define program-arguments command-line)
+
+  (define delete-duplicates! (@ (srfi srfi-1) delete-duplicates))
+
+  ;; Mes does not have port buffers.
+  (define flush-all-ports noop)
+
+  ;; Mes uses raw file descriptors for file ports.
+  (define file-port? number?)
+
+  ;; This is probably OK...?
+  (define (input-port? port) #f)
+  (define (output-port? port) #f)
+
+  ;; Fix 'dup' interface.
+  (let ((mes/dup dup))
+    (define* (guile/dup fd #:optional new)
+      (if new (dup2 fd new) (mes/dup fd)))
+    (set! dup guile/dup)))