Remove 'using std::error_code' from tools.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210876 91177308-0d34-0410-b5e6-96231b3b80d8
Remove the last uses of 'using std::error_code'

This finishes the transition to std::error_code.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210877 91177308-0d34-0410-b5e6-96231b3b80d8