Changes

Add a CMake testsuite-depends target. (#1241)

  - This target will build what is needed to run the `OMSimulator` testsuite.
    That is, it will build the `omc-diff` executable and it will also create
    `FMUs` and `SSPs` from the provided source files in the `resources/` folder.

  - The target **DOES NOT** and can not run the actual tests. It just prepares
    the required files. The actual testsing is still done using either the
    `Makefiles` in each directory or the `partest` perl script.