Correct the size of _Unwind_Exception.

To fix the alias1 exception test for clang on MIPS architecture, and
increase the compatibility with gcc, we should use uint32_t for
private_1 and private_2.

With this change, the sizeof(_Unwind_Exception) == 24 on MIPS,
and sizeof(_Unwind_Exception) == 32 on X86.

Change-Id: I75633d2fadf58a5d90a1cec76ce2458b51d0154b
4 files changed