libbb: locate PAGE_SIZE on Hurd

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

libbb/appletlib.c

@@ -26,11 +26,16 @@
  *
  * FEATURE_INSTALLER or FEATURE_SUID will still link printf routines in. :(
  */
-
 #include "busybox.h"
 #include <assert.h>
 #include <malloc.h>
-#include <sys/user.h> /* PAGE_SIZE */
+/* Try to pull in PAGE_SIZE */
+#ifdef __linux__
+# include <sys/user.h>
+#endif
+#ifdef __GNU__ /* Hurd */
+# include <mach/vm_param.h>
+#endif
 
 
 /* Declare <applet>_main() */