Add mkdir-p.

* gash/guix-build-utils.scm (mkdir-p): New function, import from Guix.

gash/guix-build-utils.scm

@@ -44,6 +44,7 @@
             grep-match-line
             grep-match-column
             grep-match-end-column
+            mkdir-p
 
             directory-exists?
             executable-file?
@@ -212,3 +213,28 @@ transferred and the continuation of the transfer as a thunk."
                                          (lambda (in)
                                            (grep* pattern #:port in #:file-name file))))
         (else (grep* pattern))))
+
+(define (mkdir-p dir)
+  "Create directory DIR and all its ancestors."
+  (define absolute?
+    (string-prefix? "/" dir))
+
+  (define not-slash
+    (char-set-complement (char-set #\/)))
+
+  (let loop ((components (string-tokenize dir not-slash))
+             (root       (if absolute?
+                             ""
+                             ".")))
+    (match components
+      ((head tail ...)
+       (let ((path (string-append root "/" head)))
+         (catch 'system-error
+           (lambda ()
+             (mkdir path)
+             (loop tail path))
+           (lambda args
+             (if (= EEXIST (system-error-errno args))
+                 (loop tail path)
+                 (apply throw args))))))
+      (() #t))))