Move everything over to TargetInfo.

I really would have liked to split this patch up, but it would greatly
complicate the lld-core and lld drivers having to deal with both
{Reader,Writer}Option and TargetInfo.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@173217 91177308-0d34-0410-b5e6-96231b3b80d8