fixes #6016 union alias trigger bad codegen (#6117)

* fixes #6016 union alias trigger bad codegen
* cpp test ok
* merging some test into one file

tests/cpp/ttypeinfo.nim

@@ -1,5 +1,22 @@
 discard """
+  output: '''100'''
   cmd: "nim cpp $file"
 """
 
 import typeinfo
+
+#bug #6016
+type
+  Onion {.union.} = object
+    field1: int
+    field2: uint64
+
+  Stroom  = Onion
+
+  PStroom = ptr Stroom
+
+proc pstruct(u: PStroom) =
+  echo u.field2
+
+var x = Onion(field1: 100)
+pstruct(x.addr)