Copy relocations are relocations to copy data from DSOs to
executable's .bss segment at runtime. It doesn't make sense to
create such relocations for zero-sized symbols.
GNU linkers don't agree with each other. ld rejects such
relocation/symbol pair. gold don't reject that but do not create
copy relocations as well. I took the former approach because
I don't think the latter is what user wants.
llvm-svn: 270525