Before this patch we would demangle abi-tagged structures as follows:
$ c++filt -n _ZN1SB5OuterC2Ev S[abi:Outer]:() $ c++filt -n _ZN1SB5OuterD2Ev S[abi:Outer]::~()
This is because Node::getBaseName was unimplemented for the
AbiTagAttr node, which meant that when we tried printing CtorDtorName
where its Basename Node was an AbiTagAttr, we'd drop the
name.