[ELF][X86-64] Use the correct base address.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@173527 91177308-0d34-0410-b5e6-96231b3b80d8
[ELF][x86-64] Add relocation string<->kind.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@173533 91177308-0d34-0410-b5e6-96231b3b80d8