Patch: _Jv_BuildGCDescr() (fix -findirect-dispatch)

[Andrew Haley]

Bryce McKinlay writes:
 > _Jv_BuildGCDescr was generating backwards mark descriptors (first word 
 > of object should be in most significant bit of descriptor). Also it 
 > wasn't taking into account the vtable pointer and sync_info fields, 
 > which should also be marked. This was causing major breakage for code 
 > compiled with -findirect-dispatch.

Hell's teeth!  You found this at the *exact same time* that I did!

Oh well.

Andrew.