Handling of linkgroups for order independent linking of subset of libraries

[teonnik]

In the following case :

links {"A"}
linkgroups "On"
links {"B", "C"}
linkgroups "Off"
links {"D"}

1. Are only "B" and "C" wrapped in --start-group / --end-group
2. Does linkgroups have to be wrapped in a filter {system:linux} or will it just do nothing on e.g. windows?