On glibc-2.36 this fails with

    genauth.c:45:12: fatal error: bsd/stdlib.h: No such file or directory
       45 | #  include <bsd/stdlib.h>
          |            ^~~~~~~~~~~~~~

This is because the file will be included if HAVE_ARC4RANDOM is true and `__linux__` is set.
However, this is wrong: arc4random is now defined in glibc-2.36 and thus stdlib.h must be included
even though HAVE_ARC4RANDOM is true.

diff --git a/xdm/genauth.c b/xdm/genauth.c
index cd2ad61..74d0ae1 100644
--- a/xdm/genauth.c
+++ b/xdm/genauth.c
@@ -40,13 +40,7 @@ from The Open Group.
 
 #include <errno.h>
 
-#ifdef HAVE_ARC4RANDOM
-# ifdef __linux__
-#  include <bsd/stdlib.h>
-# else
-#  include <stdlib.h>
-# endif
-#endif
+#include <stdlib.h>
 
 #include <time.h>
 #define Time_t time_t