[lua] dce adjustments for lua (#5479)

src/optimization/dce.ml

@@ -54,6 +54,7 @@ let keep_whole_class dce c =
 	|| super_forces_keep c
 	|| (match c with
 		| { cl_path = ([],("Math"|"Array"))} when dce.com.platform = Js -> false
+		| { cl_path = ([],("Math"|"Array"|"String"))} when dce.com.platform = Lua -> false
 		| { cl_extern = true }
 		| { cl_path = ["flash";"_Boot"],"RealBoot" } -> true
 		| { cl_path = [],"String" }
@@ -761,4 +762,4 @@ let run com main full =
 		| x :: l -> x :: remove_meta m l
 	in
 	List.iter (fun cf -> cf.cf_meta <- remove_meta Meta.Used cf.cf_meta) dce.marked_fields;
-	List.iter (fun cf -> cf.cf_meta <- remove_meta Meta.MaybeUsed cf.cf_meta) dce.marked_maybe_fields
+	List.iter (fun cf -> cf.cf_meta <- remove_meta Meta.MaybeUsed cf.cf_meta) dce.marked_maybe_fields