fix #15663 (#15839) [backport:1.4]

lib/system/widestrs.nim

@@ -214,3 +214,10 @@ proc `$`*(w: WideCString, estimate: int, replacement: int = 0xFFFD): string =
 
 proc `$`*(s: WideCString): string =
   result = s $ 80
+
+when defined(nimv2):
+  proc `$`*(s: WideCStringObj, estimate: int, replacement: int = 0xFFFD): string =
+    `$`(s.data, estimate, replacement)
+
+  proc `$`*(s: WideCStringObj): string =
+    $(s.data)

tests/stdlib/t15663.nim

@@ -0,0 +1,7 @@
+discard """
+  cmd: "nim c --gc:arc $file"
+  output: "Test"
+"""
+
+let ws = newWideCString("Test")
+echo ws