Perform zero-initialization of virtual base classes when emitting   
a zero constant for a complete class.  rdar://problem/8424975

To make this happen, track the field indexes for virtual bases
in the complete object.  I'm curious whether we might be better
off making CGRecordLayoutBuilder *much* more reliant on
ASTRecordLayout;  we're currently duplicating an awful lot of the ABI
layout logic.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@125555 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed