[PECOFF] Fix /nodefaultlib option.

/nodefaultlib argument is a path name, so that needs to be compared
case-insensitive way. Also the ".lib" extension should be ignored.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@220508 91177308-0d34-0410-b5e6-96231b3b80d8