[bug] dotnet fails to build with --symlink-install

[ooeygui]

The VSCode ROS extension builds with --symlink-install, which generates this error:

CMake Error at ament_cmake_symlink_install/ament_cmake_symlink_install.cmake:100 (message):
  ament_cmake_symlink_install_directory() can't find
  'C:/ws/ros2dotnet_ws/build/rcldotnet_common/$<CONFIG>/netcoreapp2.0/win-x64/publish//'
Call Stack (most recent call first):
  ament_cmake_symlink_install/ament_cmake_symlink_install.cmake:314 (ament_cmake_symlink_install_directory)
  cmake_install.cmake:36 (include)

(Although, vscode should offer to allow merge install ms-iot/vscode-ros#596)