Warnings on Windows when running rqt

[mjeronimo]

When running rqt on Windows, the following warnings are displayed at startup:

C:\ros2-windows>rqt
RosPluginProvider._parse_plugin_xml() plugin file "C:\ros2-windows\share\rqt_gui_cpp/plugin.xml" in package "rqt_gui_cpp" not found
RosPluginProvider._parse_plugin_xml() plugin file "C:\ros2-windows\share\rqt_gui_cpp/plugin.xml" in package "rqt_gui_cpp" not found

It seems that the plugin.xml file is not getting installed from ros2/src/ros-visualization/rqt/rqt_gui_cpp/plugin.xml to the above-mentioned destination.

Meanwhile, ros2/src/ros-visualization/rqt/rqt_gui_cpp/CMakeLists.txt has:

if(WIN32)
  message(STATUS "rqt_gui_cpp is not yet supported on Windows. Package will not be built.")
  ament_package()
  return()
endif()

If this package isn't built yet for Windows, it seems that rqt shouldn't be trying to open the plugin.xml file for it and shouldn't issue warnings about it not being found.