Improve how to redefine macro in 2004/jdalbec

Now one can do

    make clobber Ag=47 alt

to make the number of numbers on a single line 47 (of course at the same
time as defeating the purpose :-) ).

2004/jdalbec/Makefile

@@ -56,9 +56,12 @@ CSTD= -ansi
 #
 ARCH=
 
+# variable for redefining macro Ag
+#
+Ag= 11
 # Defines that are needed to compile
 #
-CDEFINE= -DAg=11
+CDEFINE= -DAg=${Ag}
 
 # Include files that are needed to compile
 #