We do not support them and fail with llvm_unreachable currently.
This is not the only target we do not support and also seems we are missing
the tests for those we have already. But I need this one for another patch,
so posting it separatelly.
Relocation names are taken from llvm\include\llvm\BinaryFormat\ELFRelocs\PowerPC64.def
This shouldn't be llvm_unreachable, since it is very reachable...
It should be, at most, an error instead (though arguably it should just do the enumFallback in that case).