Extend the change made by commit fe4b25ec2f (Teach target_* commands to
set INTERFACE properties of IMPORTED targets, 2017-09-18,
v3.11.0-rc1~433^2~2) to work with imported targets of type `UNKNOWN`.
Fixes: #19434
Note: This still does not link the object-files of the `OBJECT` library
from the right-hand side of `target_link_libraries` to the target on the
left-hand side. (In this particular case of another `OBJECT` library on
the left-hand side this would not make any sense anyway. The target on
the left-hand side has no link-step.)
Issue: #14778
Note: This only allows `OBJECT` libraries to be on the right-hand side
of `target_link_libraries` but still does not link its object-files to
the target on the left-hand side.
Issue: #14778
The proper way to use libraries is now through `target_link_libraries`
for things such as usage requirements, compile definitions, include
directories, etc. To facilitate this, allow `OBJECT` libraries to "link"
to other libraries.
Co-Author: Ben Boeckel <ben.boeckel@kitware.com>
Issue: #14778
Now, several `INTERFACE_*` properties can be set on `IMPORTED` targets,
not only via `set_property` and `set_target_properties` but also via
`target_compile_definitions`, `target_compile_features`,
`target_compile_options`, `target_include_directories`, `target_sources`
and `target_link_libraries`.
Fixes: #15689
Issue: #17197
The `add_library` and `add_executable` commands can now be called with
no source-files and won't generate a warning or error message, as long
as source-files will be added later via the `target_sources` command.
If during the generation step still no sources are associated with
targets created by such calls a useful error message will be generated
and generation fails.
Targets of type `INTERFACE_LIBRARY`, `UTILITY` or `GLOBAL_TARGET` are
excluded from this check because we do not need sources for these target
types during generation.
Fixes: #16872
