Add -help option to Darwin Driver.  Use grouping in Options table to better format help output

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@186640 91177308-0d34-0410-b5e6-96231b3b80d8
[PECOFF][Driver] Add -libpath command line option.

The logic to search a library from the library paths will be implemented
in a different patch.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@186644 91177308-0d34-0410-b5e6-96231b3b80d8