[regression] libclang no longer reports empty names for anonymous enum/struct/union

[emilio]

19e984e changed libclang behavior in a way that breaks rust-bindgen, see rust-lang/rust-bindgen#2312.

Bindgen relied on the empty name to detect anonymous records / enum / unions. Looking a bit deeper, now we don't support ancient libclang versions we could probably switch to clang_Cursor_isAnonymous and so on, but it is still probably worth flagging the behavior change in case some other code relied on that.

cc @AaronBallman

[emilio]

Actually let me confirm that clang_Cursor_isAnonymous is sufficient, it doesn't seem to be at a glance.

[AaronBallman]

Thank you for letting me know! I knew this impacted libclang when I made the changes, but I considered it a bug fix rather than a design change. If clang_Cursor_isAnonymous and clang_Cursor_isAnonymousRecordDecl do not work for you, please let me know (it'd also help to know which API you were using to get the declaration name information).