Fixes for Hurd build

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/libbb/die_if_bad_username.c b/libbb/die_if_bad_username.c
index e5e1160..d05dc74 100644
--- a/libbb/die_if_bad_username.c
+++ b/libbb/die_if_bad_username.c
@@ -8,6 +8,10 @@
  */
 #include "libbb.h"
 
+#ifndef LOGIN_NAME_MAX
+#define LOGIN_NAME_MAX 256
+#endif
+
 /* To avoid problems, the username should consist only of
  * letters, digits, underscores, periods, at signs and dashes,
  * and not start with a dash (as defined by IEEE Std 1003.1-2001).