This is essential if find package modules define imported
targets (usual for modern Cmake). Without this rerunning Cmake another
time in a non-clean build directory will abort with errors if imported
targets are used. E.g. with
```
CMake Error at /home/mblatt/src/dune/opm-2.9/opm-common/cmake/Modules/OpmSatellites.cmake:320 (add_executable):
Target "test_mpiutil" links to target "ParMETIS::ParMETIS" but the target
was not found. Perhaps a find_package() call is missing for an IMPORTED
target, or an ALIAS target is missing?
Call Stack (most recent call first):
CMakeLists.txt:308 (opm_add_test)
CMake Error at /home/mblatt/src/dune/opm-2.9/opm-common/cmake/Modules/OpmSatellites.cmake:320 (add_executable):
Target "test_mpiutil" links to target "QuadMath::QuadMath" but the target
was not found. Perhaps a find_package() call is missing for an IMPORTED
target, or an ALIAS target is missing?
Call Stack (most recent call first):
CMakeLists.txt:308 (opm_add_test)
```
This will result in multiple searches, but this should be rather fast
due their previous results being cached.
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