Fix ARM EHABI when function has landingpad and nounwind.

If the function has the landingpad instruction, then the
handlerdata should be emitted even if the function has
nouwnind attribute.  Otherwise, following code will not
work:

    void test1() noexcept {
      try {
        throw_exception();
      } catch (...) {
        log_unexpected_exception();
      }
    }

Since the cantunwind was incorrectly emitted and the
LSDA is not available.