I have found a fix to my problem. It was actually much easier than I was making it out to be. The variable CMAKE_<LANG>_LINK_EXECUTABLE does not need to be defined before calling project() as I was attempting to do by defining it as a Platform/ or in the toolchain file. It can actually be defined in the CMakeLists.txt file, after the call to project().
Defining this rule variable before the call to project() might be possible in a Platform/ file or some other way, but I had no luck with that approach.