CMake: improve handling of gecode-test

Ensure that it gets built when testing is enabled,
and that CMake actually uses said executable target,
and not some binary.

That being said, the test does not pass with assertions enabled:
Gecode#200

CMakeLists.txt

@@ -389,6 +389,7 @@ if (FLOATSRC)
 endif ()
 
 add_executable(gecode-test EXCLUDE_FROM_ALL ${TESTSRC} ${TESTHDR})
+set_target_properties(gecode-test PROPERTIES EXCLUDE_FROM_ALL $<NOT:$<BOOL:${BUILD_TESTING}>>)
 target_link_libraries(gecode-test gecodeflatzinc gecodeminimodel)
 
 add_executable(fzn-gecode ${FLATZINCEXESRC})
@@ -428,13 +429,13 @@ endif()
 
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 
-option(BUILD_EXAMPLES "Build examples." OFF) 
+option(BUILD_EXAMPLES "Build examples." OFF)
 if (${BUILD_EXAMPLES})
   add_subdirectory(examples)
 endif()
 
 enable_testing()
-add_test(test gecode-test
+add_test(NAME test COMMAND gecode-test
   -iter 2 -test Branch::Int::Dense::3
   -test Int::Linear::Int::Int::Eq::Bnd::12::4
   -test Int::Distinct::Random