Add explictly exported atoms and export R_*_COPY'ed atoms.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@194278 91177308-0d34-0410-b5e6-96231b3b80d8
[mach-o] add debugging to help explain one build bot failure

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@194280 91177308-0d34-0410-b5e6-96231b3b80d8