[jvm] add --java-lib-extern

closes #9515

src/compiler/haxe.ml

@@ -856,6 +856,9 @@ try
 		("Target-specific",["--java-lib"],["-java-lib"],Arg.String (fun file ->
 			add_native_lib file false;
 		),"<file>","add an external JAR or class directory library");
+		("Target-specific",["--java-lib-extern"],["-java-lib-extern"],Arg.String (fun file ->
+			add_native_lib file true;
+		),"<file>","use an external JAR or class directory library for type checking");
 		("Target-specific",["--net-lib"],["-net-lib"],Arg.String (fun file ->
 			add_native_lib file false;
 		),"<file>[@std]","add an external .NET DLL file");

src/generators/genjvm.ml

@@ -2886,7 +2886,7 @@ let generate jvm_flag com =
 	gctx.typedef_interfaces <- new typedef_interfaces anon_identification;
 	gctx.typedef_interfaces#add_interface_rewrite (["haxe";"root"],"Iterator") (["java";"util"],"Iterator") true;
 	let class_paths = ExtList.List.filter_map (fun java_lib ->
-		if java_lib#has_flag NativeLibraries.FlagIsStd then None
+		if java_lib#has_flag NativeLibraries.FlagIsStd || java_lib#has_flag FlagIsExtern then None
 		else begin
 			let dir = Printf.sprintf "%slib/" jar_dir in
 			Path.mkdir_from_path dir;