[hxb] writer: avoid side effects on TAnon fields type

src/compiler/hxb/hxbWriter.ml

@@ -349,7 +349,11 @@ class ['a] hxb_writer
 		chunk#write_uleb128 i
 
 	method write_anon_ref (an : tanon) (ttp : type_params) =
-		let pfm = Option.get (anon_id#identify true (TAnon an)) in
+		(* This weird thing avoids breaking #7672 on C# target, which would break by only using hxb writer *)
+		(* Likely not the right fix, though *)
+		let anon = duplicate (TAnon an) in
+
+		let pfm = Option.get (anon_id#identify true anon) in
 		let ftp = field_type_parameters#to_list in
 		let ttp = ttp @ type_type_parameters#to_list in
 		let i = anons#get_or_add pfm.pfm_path (an,ttp,ftp) in