Fix alias1 exception test (MIPS).

The _Unwind_Exception structure in GAbi++ requires 32 bytes.
But clang is generating the code which assumes
sizeof(_Unwind_Exception) is equal to 24.  This will result
in incorrect address when we are catching the exception
object with its reference type.

Change-Id: Ia3f6b55717e6f7f8f25050460c1dbb7f7a5a5232