Use error_condition from the std namespace.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@210730 91177308-0d34-0410-b5e6-96231b3b80d8
Use error_category from the std namespace.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@210732 91177308-0d34-0410-b5e6-96231b3b80d8