PECOFF: Define and use BaseReloc type instead of std::pair.
PECOFF: Define and use BaseReloc type instead of std::pair.

"first" and "second" are not easy to memorize.
Define a type to use meaningful names.

git-svn-id: f6089bf0e6284f307027cef4f64114ee9ebb0424@231614 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/lld,llvm-mirror/lld