Ensure we fence the writing of clazz to an Object post allocation.

We hold the heap lock during the calloc of an object in the GCed heap.
We do a non-volatile store following this for the clazz, this may lead to a
race where an object is allocated but appears to have no clazz.

Found investigating Bug: 7028104

Change-Id: I390ad4c7b9632127bd27393742be347b84d9269a
1 file changed