This change teaches CallInsts and InvokeInsts to maintain a set of
operand bundles as part of its operands. CallInsts and
InvokeInsts with operand bundles co-allocate some space before their
Use array to hold meta information
(OperandBundleUser::BundleOpInfo) about which of its operands are
part of an operand bundle.
The strings corresponding to the bundle tags are interned into
LLVMContextImpl::BundleTagCache. We could reference count these if
needed, but right now I don't see any need to do so.
This change does not include any parsing / bitcode support. That's
the next change.
Depends on D12455.