gnu: hurd-headers: Use --build instead of --host.

* gnu/packages/hurd.scm (hurd-headers): Replace '--host' with
  '--build'.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

gnu/packages/hurd.scm

@@ -116,7 +116,7 @@ (define-public hurd-headers
 
        #:configure-flags '(;; Pretend we're on GNU/Hurd; 'configure' wants
                            ;; that.
-                           "--host=i686-pc-gnu"
+                           "--build=i686-pc-gnu"
 
                            ;; Reduce set of dependencies.
                            "--without-parted")