Most ppc64 relocations come in six or more variants where the basic
relocation formula is the same, but which bits of the computed value
are installed where changes. Introduce the concept of "variants" for
internal relocations to support this. Since this applies to
architecture-independent relocation types like R_PCREL, we do this in
relocsym.
Currently there is only an identity variant. A later CL that adds
support for ppc64 ELF relocations will introduce more.