move utmp.h include to libbb.h

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/shell/ash.c b/shell/ash.c
index 298ba35..0bcbf90 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -4944,6 +4944,8 @@
  * Code for dealing with input/output redirection.
  */
 
+#undef EMPTY
+#undef CLOSED
 #define EMPTY -2                /* marks an unused slot in redirtab */
 #define CLOSED -3               /* marks a slot of previously-closed fd */