[Gnu] -L paths is not positional.

Looks like -L paths are not positional. They need to be added to a list of
search paths and those needs to be searched when lld looks for a library.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@195594 91177308-0d34-0410-b5e6-96231b3b80d8