Symlink install does not respect destination defaults

[cottsay]

Given a CMake installation which doesn't specify any destination arguments like this:

install(TARGETS testpkg)

CMake will determine the installation locations based on certain variables and eventually fall back to a static default.

When we symlink install, these default locations are not respected at all resulting in installation directly to the prefix directory.

Expected:

-- Symlinking: install/testpkg/lib/libtestpkg.so.1.2.3
-- Symlinking: install/testpkg/lib/libtestpkg.so.1
-- Symlinking: install/testpkg/lib/libtestpkg.so
-- Symlinking: install/testpkg/lib/libtestpkgstatic.a
-- Symlinking: install/testpkg/bin/testpkg

Actual:

-- Symlinking: install/testpkg//libtestpkg.so.1.2.3
-- Symlinking: install/testpkg//libtestpkg.so.1
-- Symlinking: install/testpkg//libtestpkg.so
-- Symlinking: install/testpkg//libtestpkgstatic.a
-- Symlinking: install/testpkg//testpkg

The logic for determining the installation destination would need to be added to ament_cmake_symlink_install_targets.cmake because ament_cmake_symlink_install.cmake.in is run as a script which doesn't have the variables needed to determine the default locations.

The most simple workaround is to specify destination locations explicitly:

install(TARGETS testpkg
  ARCHIVE DESTINATION lib
  LIBRARY DESTINATION lib
  RUNTIME DESTINATION bin
)