Fix ARM EHABI compact model 1 and 2 without handlerdata.

According to ARM EHABI section 9.2, if the
__aeabi_unwind_cpp_pr1() or __aeabi_unwind_cpp_pr2() is
used, then the handler data must be emitted after the unwind
opcodes.  The handler data consists of several words, and
should be terminated by zero.

In case that the .handlerdata directive is not specified by
the programmer, we should emit zero to terminate the handler
data.