This is done to allow access to the eeschema library
internals for purposes of test and script access, as the
DLL library has highly restrictive -fvisibility settings
that otherwise prevent the tests being able to access 99.9%
of the eeschema library functions (only a single function
is APIEXPORT'ed, therefore that's the only test we can do).
Using object libraries is a bit of a hack, and makes for
a slower link when done for multiple targets, but with the currently
supported CMake versions, it's about as good as we can get.
A better solution in the longer term may be to break eeschema_kiface(_objects)
into many smaller libraries, each of which has a much more defined scope,
rather than one big interlinked amorphous lump. This has the advantage that
each module is testable in isolation, and we get better organisation of
inter-dependencies in the codebase.
Then, the kiface DLL will gather these sub-libs and present what
is needed on the visible DLL API. Thus, we get both a testable
suite of library functions, and a restricted kiface DLL interface.