When a target uses objects from another target which provides modules as
sources, the modules provided by the referenced target must also be
treated as if they were provided by the referencing target. Add the
concept of "forwarding" modules so that consumers can use modules
created by these sources as well.
Note that this is only sensible for Fortran where module usages are
implicit as far as CMake's visibility model is concerned. C++ modules
have their own concept of visibility which does not require or support
such `$<TARGET_OBJECTS>` reuse in this way.
Ben Boeckel