--gc:arc: `catch` doesn't work with exception subclassing

[timotheecour]

bug 1:

• --gc:arc: catch ParentException doesn't work with exception subclassing

bug 2:

• nim cpp --gc:arc doesn't work either even without exception subclassing

Example

  type MyExcept = object of CatchableError
  proc gun()=
    raise newException(MyExcept, "some msg")
  proc fun()=
    try:
      gun()
    except CatchableError: # BUG with --gc:arc (regardless of c/cpp or --exceptions:goto/setmp
    # except Exception: # ditto
    # except MyExcept: # OK with `nim c --gc:arc --exceptions:goto` and `nim c --gc:arc --exceptions:setjmp`; BUG with `nim cpp --gc:arc
      echo "caught1"
  fun()

Current Output

/Users/timothee/git_clone/nim/timn/tests/nim/all/t0900.nim(94) t0900
/Users/timothee/git_clone/nim/timn/tests/nim/all/t0900.nim(89) fun
/Users/timothee/git_clone/nim/timn/tests/nim/all/t0900.nim(86) gun
Error: unhandled exception: some msg [MyExcept]

Expected Output

caught1

Additional Information

• devel 5e9ebe9
• see also nim cpp -r --gc:arc segfaults on caught AssertionError #13071
• see also nim c --gc:arc --exceptions:{setjmp,goto} incorrectly handles raise; nim cpp --gc:arc is ok #13070