Fix Fortran module race condition in build of tests
Created by: chuckatkins
Place SmallTestData_mod.f90 into an object library to avoid multiple copies of small_test_data.mod from overwriting one another in parallel builds. CMake should be able to handle this on it's own a bit more inteligently but at the moment it does not so the object library approach used here is really just a workaround but should be sufficient for what we need.