Fix alt build of 1996/eldby

The Makefile was missing a SLEEP variable which made it harder to
reconfigure the sleep time in the alt code.

Reworded the recommendation of trying alt code first.

1996/eldby/Makefile

@@ -56,9 +56,12 @@ CSTD= -std=gnu90
 #
 ARCH=
 
+# Variable to simplify reconfiguring sleep time for alt code
+#
+SLEEP= 35000
 # Defines that are needed to compile
 #
-CDEFINE= -DZ=35000
+CDEFINE= -DZ=${SLEEP}
 
 # Include files that are needed to compile
 #