close #13071 by adding test: nim cpp -r --gc:arc` segfaults on caught AssertionError (#14323)

tests/arc/texceptions.nim

@@ -0,0 +1,16 @@
+discard """
+  cmd: "nim cpp --gc:arc $file"
+"""
+
+block: # issue #13071
+  type MyExcept = object of CatchableError
+  proc gun()=
+    raise newException(MyExcept, "foo:")
+  proc fun()=
+    var a = ""
+    try:
+      gun()
+    except Exception as e:
+      a = e.msg & $e.name # was segfaulting here for `nim cpp --gc:arc`
+    doAssert a == "foo:MyExcept"
+  fun()