add testcase for #4668 (#14946)

closes #4668
closes #9463

tests/generics/t4668.nim

@@ -0,0 +1,16 @@
+discard """
+action: compile
+"""
+
+type
+  FooObj*[T] = object
+    v*: T
+  Foo1*[T] = FooObj[T]
+  Foo2* = FooObj
+
+proc foo1(x: Foo1) = echo "foo1"
+proc foo2(x: Foo2) = echo "foo2"
+
+var x: FooObj[float]
+foo1(x)  # works
+foo2(x)  # works