[lld][WinLink] Fix use-after-return and add unit tests.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@182970 91177308-0d34-0410-b5e6-96231b3b80d8
[WinLink] Add a test for Windows-style command line options.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@182971 91177308-0d34-0410-b5e6-96231b3b80d8