Remove some hackish workarounds for windows

The add_library macro for windows was using some hackish assumptions
to ensure that libraries get installed properly.

This doesn't always work as it makes the assumption that the user actually
wanted to install the target.

Better to remove this and do it properly (e.g. see https://github.com/ros/roscpp_core/pull/10)
Merge pull request #390 from stonier/patch-7

Remove some hackish workarounds for windows