There are 3 symbol types that a .bc can provide during lto: defined, undefined, common.
Defined and undefined symbols have already been refactored. I was working on common and noticed that absolute symbols would become an oddity: They would be the only symbol type present in a .o but not in a.bc.
Looking a bit more, other than the special section number they were only used for special rules for computing values. In that way they are similar to TLS, and we don't have a DefinedTLS.
This patch deletes it. With it we have a reasonable rule of the thumb for having a symbol kind: It exists if it has special resolution semantics.