Gave constant propagation phase a better identifier

main.ml

@@ -23,7 +23,7 @@ let phases = [
      "Convert bool operations");
     ("extern", Extern_vars.phase, always,
      "Create getters and setters for extern variables");
-    ("constant", Constant_propagation.phase, when_optimize,
+    ("constprop", Constant_propagation.phase, when_optimize,
      "Constant propagation");
     ("index", Index_analysis.phase, always,
      "Index analysis");