Only added gpu test sources if it is built

Author: kjetilly

CMakeLists.txt

@@ -671,7 +671,9 @@ macro(opm-simulators_targets_hook)
   target_sources(test_RestartSerialization PRIVATE $<TARGET_OBJECTS:moduleVersion>)
   target_sources(test_glift1 PRIVATE $<TARGET_OBJECTS:moduleVersion>)
   target_sources(test_tpsa_localresidual PRIVATE $<TARGET_OBJECTS:moduleVersion>)
-  target_sources(test_blackoilintensivequantities_gpu PRIVATE $<TARGET_OBJECTS:moduleVersion>)
+  if (test_blackoilintensivequantities_gpu)
+    target_sources(test_blackoilintensivequantities_gpu PRIVATE $<TARGET_OBJECTS:moduleVersion>)
+  endif()
   if(MPI_FOUND)
     target_sources(test_chopstep PRIVATE $<TARGET_OBJECTS:moduleVersion>)
   endif()