Don't use getFileOrStdin() at where we don't want to read from stdin.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@194746 91177308-0d34-0410-b5e6-96231b3b80d8
Move DOS stub data to PECOFFLinkingContext for /stub option.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@194754 91177308-0d34-0410-b5e6-96231b3b80d8