closes #18433 (#18484)

* beneficial refactoring; use system.Endianness

* closes #18433

tests/arc/tfuncobj.nim

@@ -0,0 +1,38 @@
+discard """
+  outputsub: '''f1
+f2
+f3'''
+  cmd: "nim c --gc:orc $file"
+  valgrind: true
+"""
+
+type
+  FuncObj = object
+    fn: proc (env: pointer) {.cdecl.}
+    env: pointer
+
+proc `=destroy`(x: var FuncObj) =
+  GC_unref(cast[RootRef](x.env))
+
+proc `=copy`(x: var FuncObj, y: FuncObj) {.error.}
+
+# bug #18433
+
+proc main =
+  var fs: seq[FuncObj]
+
+  proc wrap(p: proc()) =
+    proc closeOver() = p()
+    let env = rawEnv closeOver
+    GC_ref(cast[RootRef](env))
+    fs.add(FuncObj(fn: cast[proc(env: pointer){.cdecl.}](rawProc closeOver), env: env))
+
+  wrap(proc() {.closure.} = echo "f1")
+  wrap(proc() {.closure.} = echo "f2")
+  wrap(proc() {.closure.} = echo "f3")
+
+  for a in fs:
+    a.fn(a.env)
+
+main()
+