COFF: Address review comments.
COFF: Address review comments.

- Fix race condition of `Redo`
- Avoid std::distance

git-svn-id: f6089bf0e6284f307027cef4f64114ee9ebb0424@248058 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/lld,llvm-mirror/lld