Add __unsafe_cast to fix build dependency issue (#5388)

* Add __unsafe_cast to fix build dependency issue

* ninja build

Author: cknitt

jscomp/frontend/ast_bs_open.ml

@@ -25,7 +25,7 @@
 let isCamlExceptionOrOpenVariant : Longident.t =
   Ldot (Ldot (Lident "Js", "Exn"), "isCamlExceptionOrOpenVariant")
 
-let obj_magic : Longident.t = Ldot (Lident "Obj", "magic")
+let obj_magic : Longident.t = Lident "__unsafe_cast"
 
 let rec checkCases (cases : Parsetree.case list) = List.iter check_case cases
 

jscomp/frontend/ast_utf8_string_interp.ml

@@ -357,7 +357,7 @@ let concat_exp a_loc x ~(lhs : Parsetree.expression) : Parsetree.expression =
   let loc = Bs_loc.merge a_loc lhs.pexp_loc in
   Ast_compatible.apply_simple ~loc
     (Exp.ident { txt = concat_ident; loc })
-    [ lhs; aux loc x ~to_string_ident:(Longident.Ldot (Lident "Obj", "magic")) ]
+    [ lhs; aux loc x ~to_string_ident:(Longident.Lident "__unsafe_cast") ]
 
 (* Invariant: the [lhs] is always of type string *)
 let rec handle_segments loc (rev_segments : segment list) =

jscomp/main/builtin_cmi_datasets.ml

@@ -15,6 +15,9 @@
 
 (* type 'a option = None | Some of 'a *)
 
+(* Internal *)
+external __unsafe_cast : 'a -> 'b = "%identity"
+
 (* Exceptions *)
 
 external raise : exn -> 'a = "%raise"

jscomp/main/builtin_cmj_datasets.ml

@@ -25,6 +25,9 @@
 *)
 
 
+(* Internal *)
+external __unsafe_cast : 'a -> 'b = "%identity"
+
 (** {1 Exceptions} *)
 
 external raise : exn -> 'a = "%raise"